I guess you would call this a "construction tool"
My wife is making paper flower arrangements and one of her designs features a cross made of marbles epoxied together. She made a few the hard way of trying to line up the marbles on a table and asked me to come up with a better solution. This wooden jig is what I came up with.
I routed the grooves with a simple square bit on the router table, and installed screws where needed at the end and in the middle to adjust alignment and marble height.
Since the jig is tilted two directions from plumb at the same time one simply rolls down the first marble and applies a dab of epoxy. the cross arm is the same with the marble in the middle precisely positioned to intersect both lines of marbles. No fuss no muss, it makes the marbles automatically align in the right spot.