Casio BP-120 Blood Pressure Monitor

The Casio BP-120 was released in the mid/late 90s as a follow up to the BP-100 blood pressure monitor watch. The BP-120 was mainly a cosmetic update, having a square design, compared to the rounder nature of the earlier version. This particular watch is the Japanese model, with the descriptions for the buttons around the display being in Japanese text. This model was also released in two versions, the silver metallic version with a metal strap (as shown here), and a black resin version, with a black resin strap (which can be found here).

The watch uses a 1101 module (same as the other models) with an LCD display, and time & date display. The top (yellow) part of the display is a dot-matrix LCD, and the bottom section is a standard display. The watch also has sensors on the front, and built into the back of the case for measuring pulse and blood pressure. The method of pressure monitoring is based on a principle from an ECG heart monitor called PWTT (Pulse Wave Transit Time). It works my measuring the difference in time between the pulse waves from the aorta to a pheriferal artery. The change in time between these pulses is proportional to the change in blood pressure. This method can therefore only estimate the result, and needs calibration for each user. More details on the method can be found at:
http://www.nihonkohden.com/products/tech/pwtt/how.html

The manual for the 1101 module can be found here.
For other blood pressure watches, see also the BP-300 here, and two versions of the black resin BP-120 here and here.