Measuring astigmatism with directional blur

Does calculating astigmatism using edge of blur / double vision produce accurate results? can the edge of astigmatism change easily? do I have to use a test lens kit?

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Since I have started measuring the beginning of astigmatic deformation/blur and overall blur separately, I have discovered that astigmatism varies more from day to day than overall blur. This is not surprising, as astigmatism can vary quite considerably in degree, and to some extent in axis, during the course of the day. So no, it is not accurate, but the measurement you get from an opto is not that accurate either. If you have high astigmatism, a test lens kit might help, but you would have to measure at different times of the day to see if you can find any consistency.

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I find I get pretty consistent results now that I improved my measuring technique

Can you share your measuring technique?