The Omega reference 198.XXXX represents the electronic Omega Seamaster tuning fork series from the early 70's. One can distinguish 3 model ranges:

the 120M f300 Diver (date) available in black and white on different straps and bracelets (with 3,5mm thick glass crystal a working diver's watch), the 60M f300 Cone Diver (date and day-date) with crown @2 and @3 variations and available on straps and integrated bracelets, the 60M Fashion Diver (Ref. 198.0054) with a freely rotating bezel and 2mm thick glass crystal.

OMEGA Seamaster Electronic f300hz (1972)

Ref. ST. 398.0804 | Cal. Omega 1250 (ESA 9162) | Diameter 41,2mm |

This Cone (198.008) version of the f300 electronic tuning fork Omega range of watches was produced from 1971 until 1975. Stainless steel with an integrated bracelet (1187/188). Silver dial, applied Omega logo @ 12 o'clock and date @ 3 o'clock. These watches were water resistant to 60 meters.

Omega Seamaster Electronic f300hz (1973)

Ref. 398.0806 | Calibre Omega 1250 (ESA 9162) | Diameter 41mm

This "Jumbo" Seamaster Electronic f300 (198.0005) is a chunky piece. This is further emphasized by the integrated stainlees steel bracelet (1178). It has a beautiful mat aged black dial with applied Omega logo @ 12 o'clock.