JPH0159798B2 - - Google Patents

Description

[Detailed Description of the Invention] (1) Technical Field of the Invention The present invention concerns whether the display screen of a CRT (cathode ray display tube) is displayed in the correct positional relationship relative to the display frame of the display device and without distortion. This invention relates to a CRT screen quality inspection method that automatically inspects CRT screen quality.

(2) Technical background and problems Display devices used in various data processing devices using CRTs, including word processors,
If the screen displayed on the CRT is not displayed in the correct positional relationship relative to the display frame of the display device, the quality of the screen will be significantly degraded.

For example, as shown in FIG. 1, in a display device 1 for an information processing device, the operator uses the display frame as a reference to determine whether the screen is in the correct positional relationship. The screen 3 may be offset vertically or horizontally with respect to the display frame 4, or
It is necessary that the screen 3 is not tilted and has no distortion. Note that 5 is a floppy disk insertion section.

In home televisions, slight screen shifts and distortions do not cause the user to notice a significant drop in quality, but
In information processing display devices, screen shifts, inclinations, and distortions deform displayed graphs, characters, and symbols, resulting in a significant deterioration of screen quality.

FIG. 2 shows an example of a defective screen 3, in which the screen indicated by a dotted line 6 is in a correct position relative to the frame 4. Here, Fig. 2 a shows a state in which the vertical amplitude of the screen 3 is insufficient, b shows a state in which the screen 3 is tilted, c shows a state in which pincushion distortion exists in the screen 3, d shows a state in which the center of the screen 3 is shifted to the left, e This is a case where the vertical linearity of the screen 3 is poor. There are various types of screen quality defects other than those described above, and these may overlap.

Such quality defects are often caused by poor adjustment or failure, but some are also caused by other causes. For example, screen 3 is a CRT
Even if the CRT 2 is adjusted so that it is displayed in the correct position relative to the display frame 4, if the CRT 2 is not installed correctly relative to the display frame 4, the screen 3
is not in the correct positional relationship relative to the display frame 4. Therefore, it is necessary to ultimately inspect the quality of the screen after the CRT is attached to the display device.

By the way, in the past, the quality of the screen was inspected solely by visual inspection by an inspector. This not only causes problems for humans in that it causes eye strain, but also causes problems such as the quality of the test being inconsistent since it is performed by humans, and it is difficult to speed up the test. There was a problem.

(3) Purpose of the Invention The purpose of the present invention is to solve the above-mentioned problems by automatically performing CRT screen quality inspection without manual intervention, and to provide a CRT screen quality inspection that makes this possible. The purpose is to provide a method.

(4) Structure of the Invention In order to accomplish this purpose, the CRT screen quality inspection method of the present invention uses a CRT display device and a CRT screen quality inspection method.
A test pattern generating means for generating a test pattern on a display device, a reference member provided in the CRT display device to form a reference line for determining whether the screen quality is good or bad, and a reference line by observing the test pattern and the reference member. an observation means for outputting the data of the reference line and the test pattern image, and a means for calculating the judgment amount of the following definition formula of T _BO to T _HD based on the relative interval ratio in the reference line from the data of the reference line and the test pattern image. , has a quality determination means that determines the presence or absence of screen quality defects from these determination quantities, and compares the values obtained from these definition formulas with reference quantities to detect screen position deviation, screen tilt, screen dimensional distortion, etc. It is characterized by making a judgment.

T _BO = B _O /A _O , T _BL = B _L /A _L , T _BR = B _R /A _R T _CO = C _O /A _O , T _CL = C _L /A _L , T _CR = C _R / A _R T _DO = D _O /A _O , T _DL = D _L /A _L , T _DR = D _R /A _R T _FO = F _O /E _O , T _FU = F _U /E _U , T _FD = F _D ／E _P T _GO ＝G _O ／E _O , T _GU ＝G _U ／E _U , T _GD ＝B _D ／E _D T _HO ＝H _O ／E _O , T _HU ＝H _U ／E _U , T _HD =H _D / _E DHere, the vertical distance inside the frame is A, the vertical distance on both sides is B, the distance between the inside of the frame and the top and bottom of the screen is C and D, and the center, left, and right sides are The intervals corresponding to A, B, C, and D on each measurement line are A _O , B _O , C _O ,
D _O ; A _L , B _L , C _L , D _L ; A _R , B _R , C _R , D _R ;
Let E be the left and right distance inside the frame, F be the left and right distance of the screen, and let G and H be the distance between the inside of the frame and the left and right sides of the screen.
E, F, at each measurement line in the center, upper, and lower
The intervals corresponding to G and H are E _O , F _O , G _O , H _O ; E _U ,
F _U , G _U , H _U ; E _D , F _D , G _D , _HD .

(5) Embodiments of the Invention Before describing the present invention in detail based on one embodiment, the outline of the present invention will be briefly explained.

The present invention allows the display frame position of a display device equipped with a CRT and the test pattern displayed on the CRT to be
The display dimensions of the screen are measured using a camera, etc., and based on the relative dimensions of the display frame and the test pattern.
The values of position, tilt, and various distortions are determined, and the screen display quality is determined based on whether these values are within predetermined reference values.

An embodiment of the present invention will be described below based on FIGS. 3 to 8.

FIG. 3 is an explanatory diagram showing the concept of the CRT screen quality inspection method according to the present invention. When the display device 1 moves in the direction of the arrow on the belt conveyor 7 and comes in front of the observation device 8 such as a television camera, This observation device 8 observes the display screen of the display device 1 and sends an image shown in FIG. 4 to the inspection device 9.

Figure 4 shows the observed display screen images (shown as outlines for convenience of explanation), 4U, 4D, 4
L and 4R indicate the top, bottom, left, and right edges of the inside of 4, and 3U, 3D, 3L, and 3R indicate the outermost edges of the screen (test patterns TP ₁ , TP ₂ , TP ₃ , TP ₄ ) 3. The top, bottom, left, and right edges are shown, respectively. Note that each image has its top, bottom, left, and right reversed relative to the actual display screen, but this is not essential to the present invention.

Further, P ₀ P ₀ ′, P _L P _L ′, and P _R P _R ′ indicate the vertical center measurement line, left measurement line, and right measurement line of the screen 3.
The left and right measurement lines P _L P _L ′ and P _R P _R ′ are located close to the left and right edges 3L and 3R of the screen 3, and even if there is a screen position shift or screen dimensional distortion as shown in Figure 2, the screen will remain stable. is selected to be within the range.

Q _O Q _O ′, Q _U Q _U ′, Q _D Q _D ′ indicate the horizontal center measurement line, upper measurement line, and lower measurement line of the screen 3. The upper and lower measuring lines Q _U Q _U ′, Q _D Q _D ′ are located close to the upper and lower edges R _U , R _D of the screen 3, and they can be used even if the screen position shift or screen dimensional distortion as shown in Fig. 2 occurs. It is selected as shown in the screen.

Then, the distance between the top and bottom inside the frame 4 is A, the distance between the top and bottom of the screen 3 is B, the distance between the inside of the frame 4 and the top and bottom of the screen is C and D, and each measurement line at the center, left, and right. The intervals corresponding to A, B, C, and D in A ₀ , B ₀ ,
C ₀ , D ₀ ; A _L , B _L , _CL , _DL ; A _R , _BR , C _R , _DR . Similarly, the left and right distance inside the frame 4 is E, the left and right distance of the screen 3 is F, the distance between the inside of the frame 4 and the left and right sides of the screen is G, H, and E, Let E _O be the interval corresponding to F, G, and H,
F _O , G _O , H _O ; E _U , F _U , G _U , H _U ; E _D , F _D , G _D ,
Let's say _HD .

Based on these parameters, the following determination amounts T _BO to T _DL are defined.

T _BO = B _O /A _O , T _BL = B _L /A _L , T _BR = B _R /A _R T _CO = C _O /A _O , T _CL = C _L /A _L , T _CR = C _R / A _R T _DO = D _O /A _O , T _DL = D _L /A _L , T _DR = D _R /A _R , and the reference quantities for these judgment quantities are given the subscript "S" and are T _BOS , T _COS , T _DOS , T _BLS , T _CLS , T _DLS ,
Indicated by _TBRS , _TCRS , and _TDRS . Similarly, the following judgment amount is defined for the horizontal direction as well.

T _FO = F _O /E _O , T _FU = F _U /E _U , T _FD = F _D /E _P T _GO = G _O /E _O , T _GU = G _U /E _U , T _GD = G _D / E _D T _HO = H _O /E _O , T _HU = H _U /E _U , T _HD = _HD /E _D , and the standard values of these judgment quantities are T _FOS ,
T _GOS , T _HOS , T _FUS , T _GUS , T _HUS , T _FDS , T _GDS ,
T _HDS shall be indicated.

Once the model of the display device 1 is determined, the dimensions of the frame 4 and the screen 3 are determined, so the reference amount of each determination amount is uniquely defined according to the model of the display device 1.

If the quality of the display screen is judged based on the judgment amount and reference amount as described above, without depending on the absolute dimensions of the frame 4 and the screen 3 observed here, the following advantages can be obtained.

That is, in FIG. 3, when the display device 1 is observed by the observation device 8, the display device 1 is
When the display screen is observed at a position in front of the observation device 8, with the display screen facing at right angles to the direction of the observation device 8, each dimension of the observed display screen image shown in FIG. 4 has a value that is correctly proportional to the actual dimension. show. Therefore, it is possible to determine whether the quality is good or bad depending on whether or not this dimension is within a predetermined range with respect to the reference value.

However, in reality, the display device 1 is
When placed on top of the observation device 8, the observation device 8 is likely to be observed slightly deviated from the front position or at a distance, or in a so-called diagonal state where the display screen faces the observation device 8 at a slight deviation from the right angle. In that case, each dimension of the observed display screen image does not indicate the correct dimension, so it is impossible to determine whether the screen quality is good or bad.

However, the determination amount defined by the relative dimension ratio used in the present invention is such that even if there is a shift as described above between the display device 1 and the observation device 8, each dimension changes with the same relative relationship, so the Shows the same value as if it were not present. Therefore, even if there is a positional shift between the display device 1 and the observation device 8, inspection can be performed without any problem. This facilitates transportation and observation of the display device, which is very advantageous in speeding up inspections.

Next, we will explain how to inspect the quality of the screen using the judgment amount and the reference amount.If each judgment amount is within a predetermined range with respect to the corresponding reference amount, the screen quality is determined to be good. The screen quality is determined to be poor if at least one of the determination amounts deviates from the corresponding reference amount by more than a predetermined range. The predetermined range of deviation from the reference value for determining quality is experimentally determined as a range in which no deterioration in screen quality is felt.

The present invention is capable of not only simply determining whether the screen quality is good or bad, but also detecting the details of the defect.

Examples of defects that can be detected are shown below.

Detection of screen position shift Screen position shift includes both center position shift and screen tilt. Note that the screen dimensions are normal.

-1 Detection of center position deviation As shown in FIG. 2d, center position deviations include left and right center position deviations and vertical center position deviations, which can be detected as follows.

−1-1 When there is a center position shift upward T _CO <T _COS and T _CL <T _CLS and T _CR <T _CRS and T _DO >T _DOS and T _DL >T _DLS and T _DR >T _DRS ……… -1-2 When there is a downward shift in the center position This is a case where the inequality sign in the equation is reversed.

-1-3 When there is a center position shift to the left (case d in Figure 2) T _GO <T _GOS and T _GU <T _GUS and T _GD <T _GDS and T _HO >T _HOS and T _HU > T _HUS and T _HD > T _HDS ...... -1-4 When there is a shift in the center position to the right This is a case where the inequality sign in the equation is reversed.

-2 Detection of screen tilt As shown in FIG. 2b, this is the case when the screen 3 is tilted counterclockwise or clockwise.

-2-1 When tilted counterclockwise (Fig. 2b
) T _CR > T _CRS and T _CO < T _COS and T _CL < T _CLS and T _DR < T _DRS and T _DO < T _DOS and T _DL > T _DLS ...... -2-2 Tilt clockwise When the inequality sign of the expression is reversed.

Detection of Screen Dimension Distortion Screen dimension distortion includes excess or deficiency of vertical amplitude or horizontal amplitude as shown in FIG. 2a, and pincushion-like distortion in the horizontal and vertical directions as shown in FIG. 2c.

-1 Detection of vertical amplitude distortion -1-1 When vertical amplitude is insufficient (second
In the case of figure a) (T _CR /T _CRS ) = (T _CO /T _COS ) = (T _CL /T _CLS ) = (T _DR /T _DRS ) = (T _DO /T _DOS ) = (T _DL /T _DLS ) > 1... -1-2 When the vertical amplitude exceeds This is a case where the inequality sign in the equation is reversed.

-2 Detection of vertical amplitude distortion -2-1 When horizontal amplitude is insufficient (T _GU / T _GUS ) = (T _GO / T _GOS ) = (T _GD / T _GDS ) = (T _HU / T _HUS ) = (T _HO / T _HOS ) = (T _HD ] T _HDS ) > 1... -2-2 When the horizontal amplitude exceeds This is a case where the inequality sign in the equation is reversed.

-3 Detection of pincushion distortion -3-1 Detection of pincushion distortion in the horizontal direction (that is, up and down) (T _BO / T _BOS ) < (T _BR / T _BRS ) = (T _BL / T _BLS ) < 1... ...-3-2 Detection of pincushion distortion in the vertical direction (that is, left and right) (T _FO / T _FOS ) < (T _FU / T _FUS ) = (T _FD / T _FDS < 1 ...... These often occur in practice This is a method for detecting defective cases.

In addition, in the case of screen quality defects other than those mentioned above, for example, when complicated aspects of screen positional deviation occur at the same time, or when screen positional deviation and screen dimensional distortion occur at the same time, the relational expression becomes complicated. , said~
Detection is possible by combining expressions.

However, in reality, they occur less frequently, have little practical effect given the complexity of the hardware of observation equipment, and cannot be easily readjusted, often requiring the entire equipment to be re-inspected.

Therefore, in the case of a screen quality defect as mentioned above, that is, if a compound defect other than the case shown in Figure 2 (Figure 2 e will be explained next) occurs, it is treated as a compound defect all at once. It is practical to have the display device checked again.

A method for detecting the vertical linearity defect shown in FIG. 2e will be explained with reference to FIGS. 5 and 6.

When detecting vertical linearity defects, as shown in Figure 5, N equally spaced horizontal grids _{L1 to LN} are generated inside the test patterns TP1 to _TP4 in Figure 4. are used as test patterns (there is no problem in using the test pattern in FIG. 5 as the test pattern in FIG. 4, so they will be referred to as test patterns TP ₁ to TP ₄ hereinafter without distinguishing between them).

Figure 6 shows the test pattern TP ₁ shown in Figure 5.
This is a screen image when the screen 3 displaying ~TP ₄ is observed by the observation device 8. Vertically expanded for ease of understanding.

Figure 6 is an example of vertically scanning a CRT with a length of 220 mm in the Y direction with 350 dots, so the Y of the observation screen image
Coordinates are displayed as quantized values of 0.6285 mm/dot.

Each number in FIG. 6 is a value obtained by quantizing the Y-direction coordinates of the inner sides 4D and 4U of the frame 4 and each grid of the test pattern using the observation device 8 and obtaining the position image. For example, at the measurement line P _O P _O ′,
The number "53" on the 4D indicates that the observation device 8 vertically scans the screen and observes the 4D at the 53rd dot, and the number "118" indicates that the observation device 8 vertically scans the screen and observes the 4D at the 118th dot. This shows that the image L ₁ ' of the lattice L ₁ was observed. Further, the numbers (7, 8, 9) on the right side of the numbers indicating the Y coordinate of the grid images indicate the number of dots between adjacent grid images. Where the number of dots is large, the screen 3 is enlarged in the vertical direction, and where the number of dots is small, it is reduced.

By the way, since there is a quantization error and the vertical linearity distortion does not have the property of changing rapidly, it is not preferable to calculate the linearity distortion between adjacent lattice images based on the number of dots between adjacent lattice images. For example, in the case of 8 and 9 dots, it is dangerous to determine that one dot of linearity distortion exists, considering the quantization error that exists in both.

However, such quantization errors can be removed by taking the average value of many measured values, so as shown in Figure 6, Q ₁ Q ₁ ′, Q ₂ Q ₂ ′ give Q _D Q _D ′.
By dividing the interval Q _U Q _U ' into three equal parts and using the average value in these three sections, it is possible to correctly determine the presence or absence of vertical linearity distortion.

For example, in the case of FIG. 6, the average dot in the middle section is about 8.17 dots, the lower section is about 8.22 dots, the upper section is about 7.94 dots, and the reference dot is 8.1 dots. From these, P _O in Figure 6
In P _O ', the lower part is enlarged and the upper part is reduced, so it can be seen that there is vertical linearity distortion with characteristics opposite to those in FIG. 2e.

In this way, by looking at the magnitude relationship between the average number of dots and the reference number of dots in the upper, middle, and lower three sections, it is possible to determine the mode of vertical linearity distortion.

FIG. 7 is an explanatory diagram of a specific method of observing a display screen image.

FIG. 7a shows one line in one vertical scanning direction when the display screen of the display device 1 is observed by the observation device 8. FIG. At this time, nothing is displayed on the CRT 2, and the frame portion is observed by illuminating the frame 4 without projecting illumination light onto the screen of the CRT 2.

In Figure 7a, 4' is the image of frame 4 (white level)
, 4D' and 4U' show the images of edges 4D and 4U on the top and bottom of frame 4, 2' shows the image of the CRT2 screen (black level), and 1' shows the image of the back shadow (black level).
shows. Then, by binarizing using slice level SL, 4D' and 4U' can be detected.

Note that in place of the frame 4, a portion that provides a good contrast with the screen of the CRT 2, for example, the main body portion immediately outside the frame 4, may be used.

Next, leave the positions of the display device 1 and observation device 8 as they are, turn off the illumination, and display the test patterns TP ₁ to _{TP 4} on the screen of the CRT 2. The observation device 8 will display the test patterns including the grids L ₁ to L _N. image is observed. FIG. 7b shows one lattice image L' in the vertical direction, and the Y coordinate of each lattice image is determined by binarizing at the slice level SL'.

The inner part of the frame 4 and the test pattern image can be detected from these two types of images a and b, and the position data of each image shown in FIGS. 4 to 6 can be obtained.

Note that these two types of images a and b may not be obtained separately, but may be obtained simultaneously by adjusting the illumination.

FIG. 8 shows an embodiment of the CRT screen quality inspection method of the present invention.

First, the illumination unit 10 illuminates the frame of the display device 1 so that it can be detected, the observation unit 8 observes it, and the image signal for one line in the direction of P _R P _R ' (FIG. 7a) is written into the line buffer 11. do.

The edge detection circuit 12 reads out the image signal from the line buffer 11 and detects the edges 4 inside the frame 4 above and below.
D and 4U are determined and stored in the frame edge information storage section 14 via the frame/screen switching section 13.

Similarly, the upper and lower inner edges 4D and 4U of each frame 4 are obtained from the image signals for one line each in the P _O P _O ′ and P _L P _L ′ directions, and are stored in the frame edge information storage unit 14.
Store in.

Next, the illumination 10 is turned off and a test pattern is displayed on the CRT 2 of the display device 1. The observation unit 8 is P _R P _R ′,
One line each of P _O P _O ′ and P _L P _L ′ is scanned, and the grid position of each line is stored in the grid edge information storage unit 15 via the line buffer 11, edge detection circuit 12, and frame/screen switching unit 13. do.

The frame information detection section 16 obtains various determination amounts and supplies them to the screen position shift detection section 17 and the screen size detection section 18.

The lattice information detection section 19 determines the spacing between the lattices and supplies it to the lattice spacing detection section 20 .

The screen position shift detection unit 17 detects P _L P _L ′, P _O P _O ′,
The judgment amount of P _R P _R ′ is 21 on the left and 2 on the center, respectively.
2. Send it to the right part 23 and hold it there.

The screen position deviation determination unit 24 determines the deviation of the center position of the screen and the aspect of the screen inclination according to the above formulas, etc., and causes the determination display unit 25 to display the sending determination result.

Similarly, the screen size detection section 18 sends each judgment amount to the left section 26, center section 27, and right section 28 and holds them therein. The screen dimension distortion determination section 29 determines the presence or absence of vertical amplitude distortion and horizontal pincushion distortion according to the above formulas, etc., and sends the results to the determination display section 25 to display the determination results.

Between Q _D Q ₁ in FIG.
The average value of each grid spacing between Q ₁ Q ₂ and Q ₂ Q _U is sent to the lower part 30, the center part 31, and the upper part 32 and held therein.

The linear distortion determination section 33 determines the mode of vertical linear distortion from these average values and sends it to the determination display section 25.
Display the judgment results.

Incidentally, when the plane positional deviation determining section 24, the screen dimension distortion determining section 29, and the linear distortion determining section 33 cannot determine, it is determined that there is a composite defect and sends it to the determination display section 25.

Note that each of these operations is controlled by the control section 34.

The above is similarly performed in the vertical scanning direction. In horizontal scanning direction, left, right, top,
The lower parts 21, 23, 26, 28, 30, and 31 will have the names shown in parentheses.

Note that the number of measurement lines on the upper, lower, center, left, and right sides is not limited to three each on the upper and lower sides and on the left and right sides, but can be any number. By increasing the number of monitors, detailed data regarding changes in screen quality can be obtained, allowing accurate judgment to be made.

(6) Effects of the Invention According to the present invention, the quality of a CRT screen can be inspected without using a line scan camera having a special arrangement of image sensors as described in, for example, Japanese Patent Laid-Open No. 117928/1982. Everything can be done automatically without manual intervention. In addition, the inspection content is not limited to simply determining pass/fail, but can also specifically detect defects such as screen misalignment, screen tilt, and screen size distortion. Furthermore, since there is no need to strictly define the positional relationship between the display device and the observation section, inspection can be carried out easily and quickly.

[Brief explanation of drawings]

Fig. 1 is an external view of the display device, Fig. 2 is an explanatory diagram of an example of poor screen quality, Fig. 3 is a conceptual explanatory diagram of the present invention, and Figs. 4 to 6 are CRT screen quality inspections of the present invention. FIG. 7 is an explanatory diagram of the method of detecting the frame and test pattern position of the present invention, and FIG. 8 is a configuration diagram of an embodiment of the present invention. In the figure, 1 is a display device, 2 is a CRT, 3 is a screen,
4 is a frame, 5 is a floppy disk insertion part, 6 is a correct screen image, 7 is a belt conveyor, 8 is an observation device, 9 is an inspection device, 10 is an illumination, 11 is a line buffer, 12 is an edge detection circuit, 13 is a Frame/screen switching unit; 14, frame edge information storage unit; 15, lattice edge information storage unit; 16, frame information detection unit; 17, screen position shift detection unit; 18, screen size detection unit;
9 is a grid information detection unit; 20 is a grid interval detection unit; 2
4 is a screen position shift determination section, 25 is a determination display section, 2
9 is a screen dimension distortion determination section; 33 is a linear distortion determination section; 3
4 indicates a control section.

Claims (1)

[Scope of Claims] 1. A CRT display device, a test pattern generating means for generating a test pattern on the CRT display device, and a reference member provided on the CRT display device to form a reference line for determining the quality of the screen. , an observation means for observing the test pattern and the reference member and outputting data of the reference line and the test pattern image, and based on the data of the reference line and the test pattern image, the following definition formula is calculated based on the relative interval ratio in the reference line. It has a means for calculating judgment quantities of , and a quality judgment means for judging the presence or absence of quality defects of the screen from these judgment quantities, and compares the values obtained from these definition formulas with the reference quantity to determine screen position deviation, screen A CRT screen quality inspection method that is characterized by determining the tilt of the screen, screen dimensional distortion, etc. T _BO = B _O /A _O , T _BL = B _L /A _L , T _BR = B _R /A _R T _CO = C _O /A _O , T _CL = C _L /A _L , T _CR = C _R / A _R T _DO = D _O /A _O , T _DL = D _L /A _L , T _DR = D _R /A _R T _FO = F _O /E _O , T _FU = F _U /E _U , T _FD = F _D ／E _P T _GO ＝G _O ／E _O , T _GU ＝G _U ／E _U , T _GD ＝B _D ／E _D T _HO ＝H _O ／E _O , T _HU ＝H _U ／E _U , T _HD =H _D / _E DHere, the vertical distance inside frame 4 is A, the vertical distance between double-sided 3 is B, the distance between the inside of frame 4 and the top and bottom of the screen is C and D, and the center and left sides are , the intervals corresponding to A, B, C, and D in each measurement line on the right are A _O , B _O ,
C _O , D _O ; A _L , B _L , C _L , D _L ; A _R , B _R , C _R , D _R , the left and right distance inside frame 4 is E, and the left and right distance of screen 3 is F, the distances between the inside of frame 4 and the left and right sides of the screen are G and H, and the distances corresponding to E, F, G, and H on the center, upper, and lower measurement lines are E _O , F _O , G _O ,
H _O ; E _U , F _U , G _U , H _U ; E _D , F _D , G _D , _HD .