I would be careful. An iPhone watch
per se, just like any computer's clock, is not a good time standard. It only syncs once in a while with a time server on the net. It can be off by several seconds. I've seen this only recently on my MacBookPro.
Try syncing manually with a time server before comparison, to make sure your iPhone has an accurate time.
I only mention this because if you do send it in, you will need to provide some information such as "on my wrist, it runs at -2sec per day". (I think that regulating a watch according to wearing habits also applies to master chronometers).
I have a plot which shows the daily variance of my PloProf (sec/day), over nearly two years:
View attachment 312345
In the middle of the time axis (around February this year), I switched my mode of comparison from computer clock to a time server on the web. Fluctuations were much smaller afterwards. (Note that this is a "poor man's method", by comparing two readings visually. The uncertainty of each data point can be up to 1 second. But I rather spend my money on watches than on timegrapher equipment ...)
Looks like calibre 8500 is very stable, by the way
Click to expand...