Originally Posted by merc350
Sorry whats this mean?
As an example... if you set your parallax at 23y but zero at 30y, you could therefore zero at 30y whilst getting parallax error due to a bad head position, this would then mean you will not be zero'd side to side at your parallax distance, you would also not then have a datum, such as perfect centre head position as you have no idea of your exact head position when zero'ing
If alternatively you zero side to side at your 23y parallax distance you cannot get any parallax error at this distance so will be setting your windage exactly with no error, then every other distance will be zero'd for windage assuming a perfectly central head position.
It's also no use winding the parallax setting on adjustable scopes to 30y to zero side to side as the ret could move when shifting parallax.
I've seen no end of shooters trying to figure why they are missing side to side at 15mm targets around their parallax distance as no matter where their head is positioned they are going to miss the crosshairs side to side.