Ruler is inacurate by a view millimeters

If you use any type of ruler with the standard A4 checked paper at density 8, the measurements are off by a view millimeters which is really annoying when trying to draw math diagramms. I’ve been trying to solve the issue by changing the measurements of my paper and the densety of the checked pattern but it changes nothing. The 3rd pic shows my currently used paper template used in all the other screenshots. You can see the issue in the last two pictures when you compare the rulers accuracy at 0 to the one at the end of each ruler. This makes measuring objects bigger than 5 cm difficult. Like i said, the issue appears with the normal as well as the tringular ruler. But by changing the measurement settings from metric to imperial, the issue goes away (see 2nd pic). But the distances between the rulers markings are way too big with the imperial setting, so thats no option for me either. Additionally and apart from the whole measurement issue: I would really appriciate a tringular ruler that has the 0 in the middle of the longest side of the triangle like in the 1st pic below. I’ll appriciate any help given so thanks in advance!