Not surprised....but we also arent building nuclear power plants so tolerance might work without digital accuracy. Plan accordingly. Let the chain tell ya what it wants more then the grinder tellin' the chain what it should be.
I wouldn't be surprised if it was off 1-2 degrees, but nearly 5? That's a difference you can feel in a chain for sure. I also noticed the chart that you get with the USG says set the head angle at +40 for most chains. With the error in the scales factored in, that would have me grinding at 45 degrees! No wonder they have been self-feeding so well!
Silly question , but if you are referencing off the work bench, is it level ,or is it out of level ? That might be your discrepancy .
The vise on the grinder is level. Or close enough. Lol So the bench is pretty close to level as well. It might be .2 Deg out? I would have a hard time keeping things from rolling off of it if the bench had a 4 Deg slope. If I set the head to 0, the wheel is noticeably/visibly out of plumb. It's not such a big deal now that I know what's up. I can skew the numbers appropriately. It does not affect the accuracy of the grinder so much as it does the accuracy of the operator!
I use my digital level/ angle gauge all the time in the shop. Learned to not trust numeric indicators on the equipment when it counts, " measure twice cut once " There's many reason the pointers are not accurate . Mine is a Wixey. Magnetic angle gauge , set it on the table top , zero it, the to the saw blade. 90.0° is 90.0° to the saw table When it counts, I check But I'm anal, I square my squares
