I got a second hand Keithley 2015 DMM.
For a 0.014 OHM short cable (measured by another good DMM -- Keysight 34465), this K2015 showed 0.05 OHM before doing anything.
After replacing two 2200uF/35V ECap and RS232 transceiver, I also cleaned the board.
Then, for the same short-cable, the K2015 measured resistance is 0.23 OHM.
Is that because I do not clean it well?
Or, is that because I clean it too good?
I dont' what to send it for calibration due to it's too expensive.