How to tell if my zero is shifting?

[Waltech Jim]

W,

Great story, but why do you feel I must have a refresher course on the foundation of accurate shooting?

Jim

 

[Brent]

Ward,

I've heard some about this but noone can really explain it beyond what they heard. Seeing that you say POI will shift left or right with the sun at 3 O'clock and 9 O'clock respectively, this would appear that the shift is opposite the direction the sun is located, so... when the sun is overhead, one would think the impact would be low not high, as you suggest? I've never seen this effect my POI so I wonder if 1/4 MOA is a high number?