From: ep. 2.1, Elementary 6.11
Line/mention: in Sherlock, when Watson expresses excitement at his blog getting hits, Sherlock scoffs. Watson retorts, “this is your living, Sherlock, not 240 types of tobacco ash.” To which Sherlock replies, “243.”
In Elementary, Irregular member The Nose mentions reading Sherlock’s “monograph on the 140 varieties of ash,” and pointing out that his differences in Trichinopoly and Birdseye ash are wrong.
Reference: we first hear of Holmes’ monograph on the 243 types of tobacco ash in the very first story, novel-length A Study in Scarlet. It is mentioned more throughout the canon, including in The Sign of Four, where he declares,
“To the trained eye there is as much difference between the black ash of a Trichinopoly and the white fluff of bird’s-eye as there is between a cabbage and a potato.”