Peachy could be 'dry' calibrated using a standard printout (printed at actual size) on A4 paper. Suggest a square, circle and a star. Place the printout on the bottom of the empty tank and start the datum print out of blender. Peachy should exactly trace the print, if it is perfectly centralised (move it until it is). Then move the print to a datum height above the base of the bottom tank and do it again. The same shape should be traced (as long as Peachy knows the height). These standard blender prints could be supplied as a download on the Peachy website. Using paper to calibrate, is a lot cheaper than using resin.