The typical advice is to put down the rim, find the hole for valve and compare two adjacent holes which one is "higher" and which one is "lower" one (the counterclockwise hole should be higher).
The problem is with my new purchase I cannot tell the difference (maybe it is due to the fact so far I used 26" rims, now I have 28" and the distances are tad bigger between holes). I look once and I see pattern, I take a look again with different angle and I see the opposite pattern.
So, is there some reliable way to measure the difference and tell which hole is higher/lower? I would need this for my purpose but also to convince the shop they sent me incorrectly drilled rim (in correct one you have almost parallel spokes over the valve, in incorrect one the spokes are more angled making less space when using the pump over the valve).
Important note: Here and in general I am interested of testing new rims, so I cannot in any way change them or even fully unpack (i.e. remove the thin protective wrap which manufacturer glued to the rim), so if the rim is incorrect I could send it back and the return will be accepted.
The rim is DT-Swiss 535 28" and all I did so far is I took it out from the package. I looked it from the inside and from the outside as well -- but after first "reading" I also rotated rim by one hole and the previous reading was contradicted by the new one (the holes should be in high-low-high-low-... pattern) because I saw the same pattern. In short, I cannot rely on my eyes.
This is just an example of spoke crossing. The perfect rim would have valve at (for example) 12 o'clock, between parallel spokes.