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Message:: [QUOTE="chip, post: 630449, member: 19122"]Just from personal experience, one product that I make is  an aluminum alloy that supposedly contains a certain amount of different metals, we will sometimes have an assortment of odds and ends that when forming will show different qualities, when forming a 64 inch radius, I can usually get pretty close by "petting" the metal as if it were an affectionate cat, sometimes this "petting" will match a template really close, sometimes it will be over sometimes under.  Even when using machines and computor controls the metal (even if the nominal thickness is uniform) will react differently, I do not assay the metal, but I ascribe the variances to variances in the alloy. Then there is the environment, I have worked with materials that have tolerances in the millionths of an inch, that must be produced in a temperature controlled environment. After all this, even the most lustruos proof coin if looked at with enough magnification will look more cratered and pockmarked than the moon, (one of the reasons I scoff at ms-70 gradings) Another variable could be the press itself, especially if a press is hydraulic the fluids tend to be sensitive to heat, a press first turned on tends to follow a pattern that seems to me to be up to 8 thousandths deeper at first, and seems to (after the fluids are warmed) become almost cyclical, with coining the results might be almost invisible, but there still are differences.[/QUOTE]