The evaluates-to operator, ‘=>’, has the special property that any ‘=>’ formulas on the stack are recomputed whenever variable values or mode settings that might affect them are changed. See Evaluates-To Operator.
The m C
(calc-auto-recompute) command turns this automatic
recomputation on and off. If you turn it off, Calc will not
update ‘=>’
operators on the stack (nor those in the attached Embedded mode
buffer, if there is one). They will not be updated unless you
explicitly do so by pressing = or until you press
m C to turn recomputation back on. (While automatic
recomputation is off, you can think of m C m C as a
command to update all ‘=>’ operators while leaving
recomputation off.)
To update ‘=>’ operators in an Embedded buffer while automatic recomputation is off, use C-x * u. See Embedded Mode.