[didntcheck]

It's also worth considering their competitors. My experience in the UK system was that TIs were a rarity and most people used graphing calculators from Casio (if they felt the need for an upgrade from a scientific calculator at all), which were cheaper, lighter, widely available in any good stationery section, and appeared more feature-rich (better screens with intuitive menus, built-in SD card slots, and probably better processors). In particular some TIs I saw lacked graphical equation display, which would be a deal breaker, exotically when our existing £15 scientific calculators had made it a basic feature

There was no requirement from the schools or exam board to use a particular brand. In theory you could do everything you needed with a basic scientific calc like the ubiquitous FX-83GT (and many people did), and the only real rule was "no computer algebra systems" (I believe the TI-89 was given as an example of a disallowed calculator). In fact the teachers were somewhat discouraging of graphing calculators at all, saying you can get one if you feel the graphs help you, but you shouldn't need anything more than what you had in GCSE

[gnicholas]

In the US, students were allowed to use the TI-89, but not the TI-9X, which. Had a QWERTY keyboard but was otherwise identical. The 89 could solve equations, but the 85 and 86 could do the same, if you inputted them in standard form (y = mx + b). It could also solve simultaneous equations, again if you standardized the formatting. This was definitely a useful feature, beyond what scientific calculators could do.