How do you know which mainspring to order on a pocket watch? As an example, assume I have a 12s 1923 Elgin movement. The serial number being 26947394 (1923 303 12s 03n3p 7j). I have seen a procedure to measure old spring width/depth/etc, but seems to leave some things out - and you cannot order in advance of repair.
Another question - is there a less expensive mainspring winder for pocket watches?