Now that is interesting. It's not a variant that our research picked up for the Carrera table - a 2456 T in second execution. Looks like we have another line to add to the table Jeff - along with the rows for second gen manuals with earlier hands that need to go in at some point...

First off, those hands, markers and that Tachy scale all point to the watch being a good 5 or 6 years later than 1964 - all of those were different (in the case of hands and markers, they were plainer, whereas the earlier Tachy scale was red and ran 50 to 200 rather than the 60 to 1000 of this watch). But it's also the first one in this configuration I've seen, which says a fair bit about its rarity. And those hands are what I wanted to see, we have some doubts about some of the other hands that come with these watches.

In terms of an insurance value, you need to be thinking about the cost of replacement - and you could be looking for years and not find one precisely the same, so you should pitch that high. For sale value, we have seen even fairly poor condition steel first generation Carreras selling at $1750 and upwards - though we have also seen others fail to sell at that. Top quality Tachys will have asking values of around twice that to circa $4000. I have seen gold Carreras with asking prices above that, but tellingly I haven't seen them sell at those prices.

So, because of condition and the Tachy scale, consider a base price a fair bit above that lower level and a ceiling somewhere around that top price. The gold case really depends on the collector - some expect to pay more for gold, others will expect a discount to even consider gold instead of steel, which obfuscates things a bit unfortunately. So sorry to be vague but where we don't see many examples of a watch selling, it's hard to be definitive on price and I for one would rather give a wide range of valuation than be really specific without much to back it up - hope it's still of some use to you.

And now, because I've been rude and haven't even complimented the watch yet, I should do so forthwith! It looks really nice and in great condition - your grandfather was clearly a man of taste. Enjoy the watch in good health.