Calculators are divided into three classes.
(a) Communicating Calculators: These are never permitted in examinations.
(b) Non-Communicating Calculators with text storage and/or graphing capability and/or longterm memory: Instructors may permit the use of these calculators in examinations but only if students are also permitted to bring "significant amounts" of written material to offset the advantage that otherwise accrues to those with fancy calculators. To be used in an examination, such a calculator must carry a "red sticker".
(c) non-communicating calculators without the features mentioned above: Instructors may permit the use of such calculators in any examination. To be used in an examination, such a calculator must carry a "gold sticker", with the exception of the very common Casio 991 model, which may be used without a sticker. (There is pressure from the examination office to sticker the Casio 991 model too, but that is not a requirement at present.)
For further information regarding when and where to pick up a sticker refer to Calculator Classification Stickers for Examinations.