Hi folks.
I would like to share a method I discovered to calibrate without need to read and write the flash memory.
Sorry if it is not new fou you, but I searched for it and did not found the procedure explained like this.
1-Simply hold pressed the HOLD+SELECT buttons while you turn on the meter to the ohms/continuity/diode option (second position). Then release the buttons.
I am not sure if this wheel position is really mandatory, but it is described in some places as the correct method.
The meter will show "CAL" and will do some auto tests. You can abort this tests pressing select 2 times. If you let it run over, it will end the auto-tests after some minutes.
(note: after change the count config to reach 6200 counts the aut-test take much more time, then I gave up waiting).
2-Now put in the function/scale you want to calibrate (rotate the wheel and press select until you reach there), can be DCV for example.
I tested only for DCV (all ranges) and DCA (all ranges) but most probably it will work for others, like ohms and capacitance. The ACV seams to share the calibration of DCV. I did not tested ACA.
3- Now comes the main part (apparently undocumented). While you are in whatever function you chose before, you can calibrate the zero point by pressing the ZERO button (once per function/scale calibration procedure) and the gain by pressing the HOLD button (short press to decrease the reading and long press to increase the reading). However, to do so you need to feed the leads with a known integer value, once each press in HOLD will jump the reading to next integer above(long press) or below(short press). So, for example if you feed 12.00Vdc but you read 11.82Vdc, than long press HOLD while you are sure the correct voltage is 12.00Vdc and the meter will adjust the reading to 12.00Vdc (first integer above 11.8V).
-Therefore, each long press will jump the reading to next integer above, while the short press will make jump to the next integer below.
-Depending the scale you are the jump may not be an integer, however you will figure it out while doing the process.
-Pay attention to the scale you are. As DCV is autoscale you need to adjust when you are at 0.000, when you are 00.00 and when you are 000.0. You need to change the scale by changing your voltage source. The point in each range to calibrate is a personal choice. I noticed that the linearity is not so good, than I prefered to calibrate at 17.00Vdc the 60Vdc range once I will be reading values mainly from my battery bank between 12 and 24Vdc.
4-After the procedure for all functions and scales you are interested to calibrate just turn off the meter. In the next turn on the new calibration is used normally.
In the attachment you can see my flash content before(left) and after(right) calibration. Differences are highlighted. I calibrated DCV and DCA only (all ranges).
It seems that some different memory positions were changed compared to the documented positions (devydd post). My meter use the DTM0660 chip.