Omega Seamaster Aqua Terra 231.10.42.21.03.001 42 mm Blue Dial

If the listing says Aqua Terra 150M and 42 mm, the exact discontinued watch is 231.10.42.21.03.001. No calibre is published for this number, so the reference itself is what you are buying. It is not the 28 mm quartz Aqua Terra, and it is not whichever 42 mm 231.10.42.21 is still easier to find.

Four Saudi offers use 231.10.42.21.03.001. The trap is the rest of that number: 231.10.42.21.03.003, 231.10.42.21.03.004, 231.10.42.21.06.001, 231.10.42.21.02.001 and 231.10.42.21.02.002. One or two digits change the watch. 220.10.28.60.54.001 is a different size class under the same Aqua Terra 150M title.