Would that suggest that you would need the graph to hand at all times?
Or a very switched on First Officer.....!
Had this just recently. I pointed out that the temp was -72 at FL380 and he replied that it put us outside of the aircraft's envelope. After a brief "Yeh, right", we descended to FL360 and a tropical -68 . A dig through the books revealed -70 as the limit. Beers on me then........
T'bug