In the Royal Artillery, a Sub Section is a component of an artillery battery consisting of one gun, its tractor (if not self-propelled) and the gun detachment (RA), ie the crew manning the weapon. This sub-section is generally under the command of a sergeant.
A Battery "consists of 2 or 3 sections, each with two guns with their complement of ammunition wagons."
(Information taken from "Royal Artillery: Glossary of terms and abbreviations, historical and modern" by Philip Jobson).
However, as your G Grandfather appears to have been in a Searchlight regiment, the above probably doesn't apply to him!
I also have found this:
56th Searchlight Regiment, R.A. (Cameronians)(T.A.) - Highland Area, Scottish Command
HQ, 417th-419th Btys: Glasgow (from
http://www.wikiwirral.co.uk/forums/ubbthreads.php/topics/432210/2.html - you have to do a Ctrl+F searching for '56th' to find it!!)
This may also be of interest:
http://ww2talk.com/forums/topic/44898-15-anti-aircraft-brigade-ra-125-cameronians-light-anti-aircraft-regiment-ra/Getting hold of his war service records will help you immensely, and if you then post pictures of sections of them the folks on here will be only too happy to help you understand them fully.
RRTB