turrets
I do not own a Mk 4, but my big Burris XTR on my match rifle and the 10x Bushnell on my .22 trainer have index marks/hash marks on the turret "shaft". Its not that hard to come back to zero by watching the turret numbers and cross checking the hash marks. The Burris actually has a "zero" setting marked that is adjustable, the Bushnell does not.