It is possible to have any number of Calc Mode buffers at once.
Usually this is done by executing M-x another-calc, which
is similar to M-# c except that if a `*Calculator*'
buffer already exists, a new, independent one with a name of the
form `*Calculator*<n>' is created. You can also use the
command calc-mode to put any buffer into Calculator mode, but
this would ordinarily never be done.
The q (calc-quit) command does not destroy a Calculator buffer;
it only closes its window. Use M-x kill-buffer to destroy a
Calculator buffer.
Each Calculator buffer keeps its own stack, undo list, and mode settings
such as precision, angular mode, and display formats. In Emacs terms,
variables such as calc-stack are buffer-local variables. The
global default values of these variables are used only when a new
Calculator buffer is created. The calc-quit command saves
the stack and mode settings of the buffer being quit as the new defaults.
There is only one trail buffer, `*Calc Trail*', used by all Calculator buffers.