As the sun drops and the ground cools down, the earth contracts to about 75% of it's original size. So, your target was much closer later in the day.This is why, if ever you need to visit someone, you should do it in the evening so you don't have to drive as far.
Seriously though, I have Winacts and haven't noticed this (yet). They sometimes go further left as the day wears on, but I think this is due to a slight shift in gravity as the earth rotates
Or, it could equipment failure, perhaps the big nut that holds the handle!
