CDM9 has calibration circuitry, so you can just swap out laser heads.
CDM1 to CDM4 is calibrated using trimpots, which is nigh impossible without a test disc & scope.
However, I've never had a CDM4 fail... CDM1 is also supremely reliable. CDM2 hasn't as solid a reputation... CDM3 is just too rare to even bother thinking about.
Mana Acoustics Racks / Bright Star IsoNodes Decoupling >> Allo DigiOne Player >> Pedja Rogic's Audial Model S DAC + Pioneer PL-71 turntable / Vista Audio phono-1 mk II / Denon PCL-5 headshell / Reson Reca >> LFD DLS >> LFD PA2M (SE) >> Royd RR3s.