I'm using the plan i found at LittleMachineShop. Plan looked simple so i started turning the piston to the size. So after i took my supposed last cut i measured the diameter with both a caliper and a micrometer (25mm-0.01mm precision) with caliper it showed slightly(from a few 0.01 to a few 0.10mm)different each time i took measurement so i tried the micrometer,it was better. Then i checked different sections and to my surprise it was showing slightly different diameters at different sections? Am i not taking measurements correctly? Or is it caused by not locking the carriage, although when i tried to move it by hand it doesnt move?