: What's the difference between the one marked "3H" and the
: one marked "AR"- from what I can see the last
: production run of 250 had the AR marking...but both with L5100.

: Are the "AR" watches any more collectible than the
: "3H"?

: dc

The "Ar" (note lower case r) on the later watches refers to the watch being filled with argon to prevent moisture getting in - argon is denser than air but inert. It's nothing to do with the lume material, unlike the 3H markings. The Ar watches have Superluminova lume, so don't need any special markings on the dial because of it, because it's not radioactive.

The early EZM2s used tritium, though later watches are marked Hydro UX and are filled with silicone oil (the EZM2 is the dive watch application, so I guess it makes sense to go a different route than for the special forces and police models). The EZM3 is an Argon-filled watch too. EZM4 is the emergency services model, not sure about that one - I think it's just plain Superluminova without being filled with anything exotic!