I managed to snag another Seiko in pristine condition, a pulsation chronograph with ref. 6139 6020. This watch has a near perfect gloss silver dial with black outer pulsation ring. The case and bracelet are also in good unpolished condition. This one looks like another drawer queen based on its overall condition.

 

Never seen one with a pulsation ring before. Definitely never one with it just over 90 degrees off.

What’s the date of MFG I can’t make out the serial and perhaps DIBS!

 

Looks like September 1970.

 

The inner ring rotates by turning the crown - why is a matter of conjecture.
There is also a school of thought that these aren't meant to literally time blood pulses, but to calculate the number of items being produced off a production line over a period of time. Hence the alternative 'donut production timer' moniker

 

Interesting I thought the inner ring was fixed on these.

Normally tachymeters are used for production lines... but I can see a pulse bezel doing it too.

 

Outstanding information about the other use of the pulsation ring. Thanks Tritto.