Uncharted Serial Number

Roy writes: 

I have had a Gledhill Brooks clocking in clock for over 30yrs. My dad acquired it for me from the CWS Shopfitting works in Salford when they changed to electronic clocks. I may even have clocked in on this clock as they were in use when I was an apprentice joiner there from 1960 to 1964 ( I left to become an architectural technician).

The clock resides in the garage and provides a lovely background tick-tock which my wife finds too loud in the house.

I've looked at a couple of serial number listings to date it but can't find the one which is on my clock.

The number I have is:  29820 (not 29208 as on your listing).

Is anyone able to assist Roy? If so, please use the Comments to reply.