A colleague asked me how sensitive the Apple Watch was, and if it supported standing desks. (those hours should count right?)
The activity rings have evolved with each watchOS release. The key is “stand and move” or “roll”. The accelerometers and pulse measurements in the hardware are extremely precise and I find accurate as well. Apple documents the “stand” ring here: https://support.apple.com/en-us/HT204517
The Stand ring shows hours in which you've stood and moved for at least a minute. Complete your daily Stand goal by standing up and moving around for at least 1 minute during 12 different hours in the day. Even if you stand all day, you still need to move around. If you've specified that you use a wheelchair, the Stand ring switches to the Roll ring. Roll shows hours in which you’ve pushed around for at least 1 minute.
Since WATCH is worn on the wrist, if your wrist rests the same way while you’re standing as it does while you’re sitting, then that time is not going to count as “standing.”
Normally it is best to walk around with your arms swinging freely for WATCH to detect that you stood. That is why the Stand reminder tells you to move around. The current research also suggests that you need to move around to counteract the negative effects of sitting for too long.
My experience has been that at a minimum, you need to hold your arms down your sides for WATCH to detect that you are standing. That is not 100% reliable however, and it is best to take a quick walk (especially since you can no longer use your hand to type anyway).
Either way, if you keep your hands on your keyboard the entire time at your standing desk, WATCH will not detect that. Another good example is cooking/doing the dishes. You will get Stand reminders while performing those activities, which typically require standing.