Harrison, P. (1991) A Series of Papers on the Early History and Development of Industrial Time Recorders – Paper 1 – Gledhill-Brook Time Recorder Co. Ltd., England, 1912-1964
Llewellin’s Gears: https://www.llewellins.co.uk
Securitas Technology (formerly Stanley): https://www.securitastechnology.com/uk/about-us
IBM Archives: https://www.ibm.com/ibm/history
Grace’s Guide To British Industrial History: https://www.gracesguide.co.uk/Main_Page
Wikipedia: https://www.wikipedia.org
National Association of Watch & Clock Collectors (NAWCC): https://www.nawcc.org
Cincinnati & Hamilton County Public Library: https://chpl.org/online-resources
Due Time blog: https://duetime.wordpress.com
The National Archives: https://www.nationalarchives.gov.uk
Companies House: https://find-and-update.company-information.service.gov.uk
IBM History: http://www-03.ibm.com/ibm/history/index.html
IBM Hursley Park Museum: http://slx-online.biz/hursley
The Bundy Museum: http://www.bundymuseum.org
Antique Time Clocks: http://www.antiquetimeclocks.com
Wikimedia Commons: https://commons.wikimedia.org/wiki/Category:Time_recorders
Wayback Machine Internet Archive: https://web.archive.org
Further information on individual inventors, company founders, and other personnel can be found via historical census data. This is archived by the Office for National Statistics (https://www.ons.gov.uk/census) in the UK, or the Census Bureau (https://data.census.gov) in the USA.
Patent documents give full technical details and drawings of the inventions, alongside an excellent insight to the inventors and their location at the time. A selection of these documents can be viewed and downloaded via the Patents page.
Very old UK patent documents are kept by The British Library, but most UK patents from 1870 onwards have now been scanned and are available online from the European Patent Office and Espacenet, which also includes some worldwide patents. Many US patent documents are also available online using the Google Patents search engine.
The British Library: https://www.bl.uk/
European Patent Office (EPO): https://www.epo.org
Espacenet: http://worldwide.espacenet.com
Google Patents: https://patents.google.com
For time recorder ribbon:
The Typewriter Man: http://www.thetypewriterman.co.uk/supplies.html
For time recorder service and repairs:
Braintree Clock Repairs: https://www.braintreeclockrepairs.co.uk/2018/03/27/national-time-recorder-clock-repair