Hi Gentlemen,

I have come to this string a little late but I think what you are talking about is the inner edge of the crystal.

Complicated watches that have an outer ring measuring scale - say a seconds counter like the Carrera or Tachymetre like this Universal (see below) usually have a mirror finish steel ring on the inside and the edge of the domed crystal is magnified so that it is easier to read the scale. This crystal on the Universal has a metal edge, is magnified and the edge of the dial is bevelled falling away to help the tach scale look bigger and as you can see it works. If you look at this watch from an angle the tach scale is only half the width of this 'head on' picture.

The phenomena is easier to see here in this pic of an Omega Seamaster, notice how the numbers on the tach scale are much bigger on the closer edge which is more head on than the other side which is viewed at an angle. This watch has a very large magnified edge to the crystal as the watch is so small.

In the case of the Carrera its crystal is high but more of a top hat than hi domed so to get around that problem of not being able to magnify the crystal edge they sloped the seconds ring as well.

A generic crystal will also fit a Carrera that does not have an inner polished metal ring. Perhaps that is the difference you have spotted.

Don't get too carried away about it as watches are like cars there are many combinations of parts.

I hope this is what you are talking about? Just let me know if it is...

Regards

Alistair