this model was one of two programmables produced by
commodore in 1977.
similar in style to the p50 but with a few more functions and extra
program memory, the pr100 has 10 memories and 72 program steps.
unfortunately, the steps are recorded keystrokes so that *`f' *or *(inv)*
keys equire storage and *goto xx* is 3 steps.

there are 45 keys which is sufficient for most functions to be on their
own. the presence of an *inv* key means that some functions like *e^x*
and *10^x* could have been expressed as *inv ln* and *inv log*.
the display is quite nice with 8+2 led, the 6's and 9's look unusual today
and the exponent digits are tastefully reduced in size.

the unit is powered internally by 3 rechargeable AA cells (not
removable), or the external mains adapter which is 6v. (note:
if the internal cells are dead and are removed, use a separate 4.5v dc
supply **not** the original).

there is no algebraic precedence (lame) and parentheses work to four
levels with no implied multiply. otherwise there is a good scientific
function set including hyperbolics, 2d stats with regression slope and
intercept, unit conversions and combinations and permutations. the latter
work in a peculiar way using *m9*. for example to calculate *52c13*;
type *13 m 9 52 Cnm*.

programming is effected by a mode switch to either of *clear*, *load*
or *run*. in *clear* mode, memory locations can be overwritten
by *nop* or the whole program memory erased. *load* mode records
keystrokes overwriting memory locations. the *back*, *step* and *goto*
keys can be used to reposition the step for overwriting. *run* mode
is normal operation.

conditional and unconditional jumps are possible with *skip*
jumping over the next instruction (key or *goto xx*) if the current
value is negative (ie skip if neg). the manual describes some creative use
of skip for other conditions. eg *n1=0* is *n1 x^2 +/- skip*
(n=0) (n!=0). pity there's no *x^2* key.