Standing distance for A4 snellen chart?

Hey guys, I have a question about the snellen chart. I have found two snellen charts online which can be printed on A4 size paper. But one of them says 10 feet chart and other says 2.8m/9feet measuring distance.

One of them mentions a "formula i.e -measure the height of the letter E (first line, 20/200) in millimeters. Then, divide the value of this measurement by 88. Finally, multiply it
by 6. The result shows the distance at which you must be placed, in meters. E.g. (42/88) x 6 = 2.8 m/9ft.

By using this formula both the charts printed on a4 size paper measures the same. The size of " big E" is same on both charts. If anyone has used home printed a4 charts please suggest how do you measure the distance.

Thanks

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I think it is most important that you stand the same distance all of the time, and control your lighting. So I would suggest pick one and stick to it. Also keep in mind that while more convenient, a 10 foot chart is over all less accurate than a 20 foot chart. But the point it having a means to gauge improvements and either will work for that.
Probably more than you bargained for but I just did a video on measuring that might help you as you get going… https://youtu.be/QyF5J6-BJZI

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I think it is most important that you stand the same distance all of the time, and control your lighting. So I would suggest pick one and stick to it.

  • That was my actual question… they both are ment to be 10ft charts, but one says 10ft on it and has different set set of lines and other one is “meant to be 10ft” too but has instructions that when printed on A4 paper ( because printers can be defaulted to different settings etc) just to make sure the right standing distance one uses the above mentioned formula. So I am confused because as the “E” on both charts measure the same in height does it mean that after printing I use the above formula in order to get the correct distance. Because the difference is of aprox 1ft.
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The 9ft (2.8m)chart and the formula I mentioned in my initial post is the chart as on EM wiki.

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I understood your original post when I responded. And, I stand by my response. Usually we stand at the distance the chart indicates. Though it doesn’t surprise me there is no discernable difference in the point size on the font for at least some of the lines. At a difference of a foot for chart distance I imagine the letter size is so close to the same it is difficult if not impossible to measure the difference.
Personally I would pick the farther, 10 foot distance, because being a little harder on your measurements is a good choice over all. Consistency is the most important element of your measurements. Don’t over stress the little details, like what turns into fractions of millimeters over a distance. As long as you use the same chart at the same distance in the same light conditions, you will succeed in tracking your vision progress.

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Maybe I missed something but are you only measuring the large E? I would only consider the 20/20 to 20/40 lines as that’s where you will likely be measuring with correction.

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The formula given to determine the distance of your chart requires the length of the large E as its input. By manipulating the scale of the pdf printout, you can change the distance of your chart.

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I understand that. I am just saying I would double check the much smaller letters. I have little faith in my printer, but yours is probably fine.

And as earlier said by @Lloydmom, consistency is the important part. Distance and lighting being key elements.

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@preetgurpreet, I guess you printed this Snellen.

These lines are supposed to be scaled properly like an opto’s Snellen.
If you printed this out in original size (not with “fit to page”, etc), then the letter E is 42mm tall and you’ll have to stand at 2.8m from it (at 286.36cm to be precise).
If the letter E is not 42mm, then use the formula to get the distance to use. (e.g. 44mm tall letter E = reading from 3metres; 40mm tall letter E = reading from 2.72metres, and so on)
With the 3 or 6 m Snellens, 5 or 10 cms do not really matter. The ultimate goal is not “just to be able to read it”, but to see the letters clear and sharp.

This is a 6m Snellen:


If you print it out correctly, the 1cm mark should measure 1cm exactly and then you’ll read it from 6m.
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I like this 6m chart. The 1cm scale line is ideal. Thanks for posting as I hadn’t seen this.

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Thanks for the reply… exactly the explanation I was looking for.

Thanks everyone for your input. If was measuring myself it wouldn’t have been a problem standing at either 10 or 9 ft, but I use this to measure my 6 year old and being at 9 or 10ft makes a huge (almost a line) difference for him and when he reads a 9ft he can almost clear one whole line, which is like a confidence booster for him. I oviously don’t want to “cheat” too by making him standing at closer distance ( if 9ft is not the correct distance). That was the sole reason to get the distance clear. Thanks to all of you who took time to respond back. Thanks

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