Prince Haram's Tiller
On board the Kite, this is an enigmatically-titled lever that, in the absence of Leonard of Quirm, neither of the other two crewmembers has the faintest idea of the purpose of. With an imminent crisis looming - ie, uncontrolled re-entry into the Disc's atmosphere and an awful lot of unforgiving ground coming up to meet them 'very, very' quickly, Ponder Stibbons is at a loss to advise. However, he has just, rather unwisely, denigrated the value of an arts-based education where Vetinari can hear it. Vetinari, a product of an arts-based education, suggests Ponder tells the crew to pull Prince Haram's Tiller. Ponder relays the suggestion, Rincewind pulls the lever, and the Kite levels out into free flight. Vetinari then affably tells Stibbons that there is an old myth, derived from Klatchian folklore, about a Prince Haram who devised an ingenious way for his ship to safely steer itself on long journeys, while he slept. But then, one whose education has been purely technical and scientific, and deficient in areas such as languages and history, is hardly likely to be aware of that...
Prince Haram's tiller is therefore what we might describe as the autopilot.
Annotation
There is a readable discourse dating from the 1950's but still relevant today, called The Two Tribes, which describes and deplores the way the educational process in Great Britain - almost uniquely in the developed world - forces able school pupils to make a prematurely early choice between "Arts" and "Science" streams. Even as early as age fourteen, the British pupil is then progressively locked firmly into either Arts or Science, and becomes as firmly embodied in that stream as a Hindu is in their caste, or inhabitants of the old South Africa were embodied acording to their skin colour. Especially at the A-level stage, the pupil must choose to specialise in all Arts subjects or all Sciences: mixing the two is not permitted and is looked on with as much horror as, say, a Boer who seeks to marry into the Zulus. The net result of this is a system where Britain has a great number of Arts grads who might be up to speed in English Lit or History, but who at age 21 last saw the inside of a laboratory at age 15 and who are woefully science-illiterate. Worryingly, a lot of these people get into government. Similarly, we have science grads who last read a novel at school and whose foreign language skills, viewed as belonging to Arts, have atrophied. These are the Two Tribes, whose stereotyped opinions of the other are illustrated by the interaction between Vetinari and Stibbons.