GCA
I never worked a full GCA, (only Half-mile SRAs on Plessy 424), but Aldergrove still had a "Federal" (Gillfillan [?]) a wartime American GCA when I was there about 1965. Rumour had it that, when Nutts Corner closed and Civil ATC took over Aldergrove, the Divisional Tels Office forgot to asses the equipment needs until too late and that when they found they had no suitable radar, they asked the RAF to leave theirs, a mobile MPN11. The reply, "Too late, Mate, it's on the boat already" caused the old "Federal" to emerge from retirement. (To be fair, the MPN11 had several features not familiar to civil controllers including Logarithmic rather than linier PAR displays so the high priced help at Division had some real worries)
The whole GCA (Surveillance and PAR) was worked from a "train" of trucks which had to be moved and set up for each runway so a runway change was a real circus and not undertaken lightly! By "worked from" I mean literally, the "Search" and "PAR" Controllers and the "GCA Tracker" sat in a lorry trailer. The one at Aldergrove had, rumour again, been "tropicalised" for the Middle East with lots of extra holes cut in it to improve the ventilation! Just the thing at Christmas 1965 with a howling gale blowing, a foot of snow on the ground and a sub-zero OAT! No wonder the crew spent as much time as possible in the tower, and only went out when it was really necessary!
The point that this ramble is leading towards is that, on this equipment, elevation was "tracked" by a "Tracker" (no surprise there then!) this was a specially trained (and paid!) ATCA who kept a cursor centred on the aircraft response on the vertical scanning radar, this gave a read out, in feet, on a meter alongside the PAR controller's horizontal scanning display, he (always he in those days) had no direct sight of the elevation display but could pass glide-path information from the trackers read out and abort the approach if it went out of limits. The tracker had to report if there was insufficient response to track or she (usually but not always she in those days) lost contact, in that case the controller could continue, with the pilots agreement, in azimuth only with, of course, higher limits. The most dangerous thing that could happen was a Tracker following something they thought was a real response, they were, very fiercely, taught never to continue if there was any doubt. Perhaps the best encouragement to good performance was sitting a few feet to the right of an active Runway, as an authorised obstruction, and running the same risk as the Aircrew after a poor approach!
The Type 2000 PAR which remained at the London Airports for several years later, was the PAR element of the GCA remoted into the ops room, and with the Tracker replaced by an elevation display in front of the Controller, who, thankfully, was no longer burdened by outdoor clothing!