"Having two different metals in intimate contact will increase the likelihood of oxidation, so contrasting colours should be combined with caution."

""Ever-newer waters flow on those who step into the same rivers." Heraclitus"

"They were not magnetic. The lid was just wedjed on the stem."

"Once I disassembled the lid of a perfume bottle. There were two metalic weights glued inside. It did feel expensive."

"Actually now that I re-examine my prototype I see that the circles did intersect if the laser beams were not parallel but the tilt required to make it noticeable was too much so I didn't pursue that idea further. So yes in principle it works. "

"I had the same idea a couple of years ago. The problem is that there is only one center of rotation so all circles (or ellipses) are always bound to be co-centric and never intersect each-other. I don't know how they projected the static inner circle on the video demo. I couldn't find anything about self adjustment in the patent text either. It is still working for the depth although there are much simpler ways of takling that. The result with the circles is that they are perfect circles when perpendicular but become ellipses when tilted. The problem is that depending on how  you tilt your head circles can look like ellipses and vice versa so it was not much of an aid. "