Hi Philflies
The 3/4 tab mounted by the #4 EGT indicator had in fact nothing to do with the EGT indication at all. It wasa reheat capability indicator and was set by the crew prior to take off. Set to 4 meant that all 4 reheats were required for take-off (and if one failed it then meant that the take-off should be rejected). Set to 3 it meant that a single reheat failure could be tolerated and the take-off could continue.
I hope this helps Philflies.
Oh and check out the website
BRINGING CONCORDE G-BOAC BACK TO LIFE - Welcome The fat lady aint singing yet. Also check out the Concorde comes alive thread here too.