I think taking a few bellweathers is a great idea Jeff, else the price guide could well become a hiding to nothing needing constant updating to reflect the market.

As well as the letter codes, which work well, maybe we could give a "% of bellweather X" price for different models - in that way, it would passively track the market and only the bellweather prices would need the frequent updates.

One question on the choices - do we see much variation across the colourways for the Silverstones in terms of price? I'd have to go back and study, but I can't say I've seen much difference in favour of a particular colour given watches in equivalent condition. I'd be tempted to lump all the Cal 12 Silverstones together, which gives a bigger sample size too. No proof, but I suspect some of the one-off spikes are someone "completing the set" with a particular colour... :)