With leads shorted display reads 2.4mOhms. There is no way to calibrate unit. Other than that its readings of higher internal resistance are consistent.
Good product, but doesn't reach the claimed accuracy at very low internal resistances. There seems to be a internal error of 1,8-3mOhm in the measurements which changes. This makes it useless for measuring very low internal resistance batteries. It seems to be accurate for slightly higher IR's though as tested to a brand new Samsung 25R and readings matched the data sheet.