As you already know, it's a Rado Diastar.
The case is Tungsten Carbide - scratchproof.
It dates somewhere between 1965 & 1975, I think. Rado will have put a serial number on the movement and from it the watch can be dated more accurately. Uncrew the caseback and post some more pictures please.
I've not seen that case style before, I like it. Nice watch!
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