It really is LM108 and LM112 (internally compensated) and there is absolutely no trick there. It has 1nA input bias that's reasonably secure with temperature as in the majority of bipolar opamps simply because β really increases with temperature. Later on iterations like LT1008/LT1012 or OP97 pushed it right down https://heraclitusy233bws8.wikifrontier.com/user