3065. Seiko. A stainless steel automatic calendar slide-rule calculator chronograph bracelet watch Reference: 6138-7000 Date: Circa 1972 Movement: 21-jewel Cal.6138B automatic Dial: Black, luminous baton hour markers, blue subsidiary dials at 12 and 6 for 12 hour and 30 minute recording, day and date apertures at 3, black tipped white pointed baton hands with luminous inserts, yellow centre chronograph hand Case: Brushed and polished cushion form, screw down back, bi-directional bezel with black slide-rule calculator insert, No.474246 Strap/Bracelet: Fitted stainless steel link Buckle/Clasp: Signed folding clasp Signed: Case, dial & movement Size: 44mm Reference 6138-7000, the "Slide Rule Calculator" wristwatch was introduced in the 1970s. In addition to the chronograph function, the "Slide Rule Calculator" features a calculator function, hence the nickname. The wearer can utilize the slide rule double bezel to complete mathematical equations.