Looking for calibration manual for Digimess/Grundig DM100

[Decee1]

Hello,

I got this Grundig DM100 that i am trying to calibrate. Right now it is 7.3mV out of spec which i would like to fix.
Anyone got a calibration manaul for it or at least can tell the golden button/command you need to press so i can calibrate the voltage range?
It is primarly the DC range i want to calibrate, i don't have any AC reference but i do own a high precision Voltage Reference and 0.05% 10K resistor