For what it's worth, I thought that I'd share this interesting letter from Waltham to their speedometer service stations.
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There's a 42 Waltham speedometer on eBay right now. Something odd is all of the NOS speedometers I've seen recently have a solid red needle. To my knowledge the factory needle was gold with a red tip and red base. Never have been able to find out when or why that was the case.