Welcome to the forum! Glad to read about your
purple gauge plum. @ztom had mentioned the smaller size before on this old thread Gauging Green Gage .Have no real world experience with the purple gauge but i do grow the green gauge. Most of us really enjoyed the old green gauge when they were more common at the store many years ago in my childhood. There are fewer gauge plums grown today than there once was. They are very hard for me to grow here. The quality is very high on the gauges. There are gauges grown that are not what we consider gauges at all but the previous post will describe their observations in more detail. There are different strains of gauge plums by the same name.