G-force is self setting for the actual G-force number, though you can manually change it. G-force needs to have either or both D and I to have a value, then it will calculate the G-force and show its on the screen. If D and or I is on, the G-force will calibrate and show the new number when you change the base RPM.
If you want to check the sensor settings, you need a level pad, or a place where you can level the plane accurately, and that includes the mount in the plane. The C number is factory set. It has to do with the electronics of the sensor, so the C is matched to the sensor. C and Y may be slightly different for different timer sensor pairs. If you haven't changed C, then Y should equal C when all is level along the fuselage length or pitch axis, as you stated. Y should match C very closely, usually within 1, maybe 2. X is less critical and a value is not stored, nor is it related to C. If you have a level pad, or the plane level along the wing/roll axis, you will see X. I try to record the X, Y and C numbers checked on a leveled pad before install. Then I can check to make sure that nothing has changed.
If you crash a timer sensor, then you might want to check to see that Y and C are still equal. If a crash changed the value, I suspect that more would be wrong than a shift in the sensor C/Y.
I hope that helps. I will try again if not :)