K8055 analog inputs not correct

The digital to analog readings appear to be correct although 255 gives 4.67v not 5v.
For an analog input of 3v on the analog inputs I get a digital reading of 90 which is way out. It should be 3/5 *255=153. What is the problem here?
Another thing I don’t understand is the power being supplied from the usb port. This must be at least 5v to get the 4.67v I measured with the multimeter. My previous understanding of power from a usb port is it is around 3v. If it was greater than 5v an onboard regulator on the k8055 could bring it down to 4.67v.
I have just started using this board although I have had it for many years. I didn’t get past the demo but now I would like to be able to program it. I have worked with arduino programming and have made quite a few programs on the nano board.
Can anybody clarify the above matters. thanks.

What reading do you get with other voltages e.g. 1V, 2V and 4V?

USB voltage should be 5V +/- 5% (4.75V to 5.25V).
If you have K8055N, the regulator on the board regulates it to 3.3V.

1.239v 34 should be (1.239/4.67) *255=67.654
1.775v 51 should be (1.775/4.67)*255= 96.92
3.93v 120 should be (3.93/4.67)*255= 214.59
These are the results I get for other analog inputs. Can these figures be explained or what is wrong here?
Should I be using an external power source to the board? But there doesn’t seem to be any provision for an external source on the board.

The readings look very linear.
Very strange, if the reading at 5V is 255.

Please check the results between 4V and 5V.

Please make sure the trimpots ATT1 and ATT2 are in max position.

No, there is no option (no need) for external power.