There are four working registers (x y z t) which are known as the stack, four general purpose memory registers, and one expanded register for displaying long values that are in the x register. The working registers are in the rectangular field at the top left of the calculator. The x register is on the bottom, and is the main entry register. Above it are the y, z, and t registers.
The [Rup] key rolls the registers up (x->y, y->z, z->t, t->x).
The [Rdn] key rolls the registers down (t->z, z->y, y->x, x->t).
A function that uses registers x and y and puts a result into the x regis-ter, drops the stack (t->t, t->z, z->y), keeping the t register value in the t register. Thus the t register value can be used as a constant.