Calc saves certain values after they have been computed once. For
example, the P (calc-pi) command initially “knows” the
constant ‘pi’ to about 20 decimal places; if the current precision
is greater than this, it will recompute ‘pi’ using a series
approximation. This value will not need to be recomputed ever again
unless you raise the precision still further. Many operations such as
logarithms and sines make use of similarly cached values such as
‘pi/4’ and
‘ln(2)’.
The visible effect of caching is that
high-precision computations may seem to do extra work the first time.
Other things cached include powers of two (for the binary arithmetic
functions), matrix inverses and determinants, symbolic integrals, and
data points computed by the graphing commands.
If you suspect a Calculator cache has become corrupt, you can use the
calc-flush-caches command to reset all caches to the empty state.
(This should only be necessary in the event of bugs in the Calculator.)
The C-x * 0 (with the zero key) command also resets caches along
with all other aspects of the Calculator’s state.