@penstruck The cuff should be modestly snug, but not 'snug'. It is supposed to take up any gaps by inflating, over-inflating, and then gradually releasing the pressure while the sensor is more firmly pressed against the radial artery, just above your inner elbow.
When I calibrate my Samsung Galaxy watch for its BP measurement app (also does ECG, blood O2 sat, and the newest version does skin free radical assessment to provide guidance on better eating habits...yes, it's true!), the instructions say to use the calibrating cuff on the opposite arm....the OPPOSITE arm...of the one where the watch is located. If you think about it a bit, in order to get certified by the (Canadian in my case) government to have the app activated and available to customers, the data must show the certifying body that the measurements by the watch are highly veridical. That is to say, they closely match the regular cuffs when they are calibrated with one of the widely available cuffs sold here and there. If the cuff is to be worn on the opposite arm, then the two arms must be highly correlated in terms of their resulting measured BP. I'm not saying there is absolutely no difference; down a flexible pipe of endothelial and lumen tissue that comprises blood vessels, you'll get lower and lower readings the further you get away from the heart. But the cuff on one arm and the watch on the other are pretty close, and at about the same height as well. In fact, the cuff is about six inches higher if both arms are properly resting on a table in front of you.