The GPA was developed by Sinclair in late 1974 for Gillette, the razor company. It was a short-lived model but formed the basis for the Sinclair Oxford 100, the first of Sinclair's Oxford range, which was launched in Spring 1975.
The Gillette model has a slightly cruder plastic case. The moulding on the Sinclair Oxford is better and slightly more rounded. This has been designated Oxford case type 1 on this site, and is always coupled with an LED display.
Later calculators in the Oxford range had a more stylish, more rounded case, ususally coupled with a green VFD display. This has been designated Oxford case type 2 on this site and can be seen on the other Oxford pages.