Snap Guides will reset the relative value to 0 along the last element snapped to.
It looks like in the example you have snap guides turned on and you snapped to your 45degree line, making the relative measurements from the snap guide line.
I do not use snap guide for this reason.
I think that the parallel line symbols is lost in the background image and also because the parallel lines are drawn at 45 degrees,
but you can see the light blue circle in the middle and the arc segments.
snap guides on - measure from snap guide
snap guides off - measure from horizontal
Archicad will keep going until it gets to 180 with polar coordinates.
unless your are using the local/relative grid system, then those are measured from the local grid.
Still looking?
