Marking A Siteglass?

[Bobby_M]

I gave one very plausible reason. The vessel tilting slightly away or towards the sight tube location at various brew times. The vessel needs to be level during calibration and use.

 

[Sockmonkey]

I ended up using some 1/8" pinstripe tape (thanks to whomever recommended it) and it looks very nice. Seems to stick very well, yet will peel off easily if needed.