OK, I connected PD0 of my mega324pa(which is a configuration pin, pulled up to 5V, not used in m-firmware) to the test button, and can now use the test button properly. I did the Test, and Adjustment(now with the 1.49m) number of times, completed successfully, and saved in Profile1.
However the issue persists: 1. Zener diodes over 10 V are measured perfectly, below 10 V(or thereabout) are shown as ~1/4th of their voltage.
2.Resistors are shown in a very strange way: I put a brand new 10 kOhm(which measures 4247 Ohm after Adj) multiturn pot, and starting from 0 slowly go up. I get this in Ohms: 0.91, 70.5, 535.6, 960.2, 1224, 1610, 2104, 2424, 2601, 11.59k, 12.72k, 14.07k, 15.23k, 16.60k, 18.20k, 2418, 2569, 2854, 3043, 3329, 3615, 3862, 4187, 4322(at the end).
I.e. going linnearly, albeit low, then for a while overshooting by double, then back to low, and finnishing at around half the actual value.
Please be aware that this is NOT A FIRMWARE ISSUE, since it had a similar behaviour with the original Chinese firmware.
I would like an opinion whether this is a hardware defect(why does it complete the Adjustment then?), or a wrong port pin specified somewhere(checked number of times, schematic is very similar to the T7 in the Clones memo)?
I have checked the resistance of the 3 probes, and the readings are practically the same to GND and VCC for all 3. Also the resistance of the 3 680 Ohms, and 470 kOhms are within 0.1% of each other.