2) 5500 Explorers came as two variants: Precision and Super Precision
3) I'm 95% confident that all original (not redialled) Precision variants were fitted a 1520 movement and that all Super Precisions had the 1530 movement.
4) The 1530 movement was also used in Rolex chronometers e.g. the Explorer 5504
5) No 5500 Explorers were ever certified Chronometers (one wonders why those fitted with the 1530 were not).
6) Genuine examples were produced only from 1958 to 1967
7) Some 5500 Explorers have the notorious "underline" and whilst I accept that the current "registration mark" theory for their existence is probably correct, I have seen an example with an underline but no overprinting which does tend to question it.
8) Most 5500 Explorers have tritium activated lume (I think that some very early ones may been radium activated) and the tritium types have the T<25 marking - but some have this marking in duplicate, symmetrically placed either side of the SWISS marking. Does anybody know why this duplication happens as I think it is only apparent in about 25% of cases?
9) I think that all examples were originally fitted with the 6635 expanding-link link bracelet, although most will long since have had this replaced with something else. Can any one confirm that 6635s were universally fitted as original equipment?
10) There is a widespread belief that 5500 Explorers were only sold through the NAAF ( British equivalent to the PX) to British serving officers. I do know for a fact that this is incorrect - though I am willing to agree that some of them might have been marketed that way.