Basically all the lines should look equally sharp when your vision is corrected. In my case - if I don't wear glasses and move close enough to see it clearly - the horizontal lines have a shadow going upwards, where as the vertical lines are sharp. The shadow is strongest on the 0 degree and 180 degree lines, meaning I have an astigmatism at one of those.
This doesn't tell you what the correction should be, but it tells you if you have it.
Take a look at this chart:
https://static2.feelgoodcontacts.net/images/astigmatism-degr...
Basically all the lines should look equally sharp when your vision is corrected. In my case - if I don't wear glasses and move close enough to see it clearly - the horizontal lines have a shadow going upwards, where as the vertical lines are sharp. The shadow is strongest on the 0 degree and 180 degree lines, meaning I have an astigmatism at one of those.
This doesn't tell you what the correction should be, but it tells you if you have it.