The `M-%` (`calc-percent`

) command takes a percentage value,
say 5.4, and converts it to an equivalent actual number. For example,
`5.4 M-%` enters 0.054 on the stack. (That's the `META` or
`ESC` key combined with `%`.)

Actually, `M-%` creates a formula of the form ``5.4%'`.
You can enter ``5.4%'` yourself during algebraic entry. The
``%'` operator simply means, "the preceding value divided by
100." The ``%'` operator has very high precedence, so that
``1+8%'` is interpreted as ``1+(8%)'`, not as ``(1+8)%'`.
(The ``%'` operator is just a postfix notation for the
`percent`

function, just like ``20!'` is the notation for
``fact(20)'`, or twenty-factorial.)

The formula ``5.4%'` would normally evaluate immediately to
0.054, but the `M-%` command suppresses evaluation as it puts
the formula onto the stack. However, the next Calc command that
uses the formula ``5.4%'` will evaluate it as its first step.
The net effect is that you get to look at ``5.4%'` on the stack,
but Calc commands see it as ``0.054'`, which is what they expect.

In particular, ``5.4%'` and ``0.054'` are suitable values
for the `rate` arguments of the various financial functions,
but the number ``5.4'` is probably *not* suitable--it
represents a rate of 540 percent!

The key sequence `M-% *` effectively means "percent-of."
For example, `68 RET 25 M-% *` computes 17, which is 25% of
68 (and also 68% of 25, which comes out to the same thing).

The `c %` (`calc-convert-percent`

) command converts the
value on the top of the stack from numeric to percentage form.
For example, if 0.08 is on the stack, `c %` converts it to
``8%'`. The quantity is the same, it's just represented
differently. (Contrast this with `M-%`, which would convert
this number to ``0.08%'`.) The `=` key is a convenient way
to convert a formula like ``8%'` back to numeric form, 0.08.

To compute what percentage one quantity is of another quantity,
use `/ c %`. For example, `17 RET 68 / c %` displays
``25%'`.

The `b %` (`calc-percent-change`

) [`relch`

] command
calculates the percentage change from one number to another.
For example, `40 RET 50 b %` produces the answer ``25%'`,
since 50 is 25% larger than 40. A negative result represents a
decrease: `50 RET 40 b %` produces ``-20%'`, since 40 is
20% smaller than 50. (The answers are different in magnitude
because, in the first case, we're increasing by 25% of 40, but
in the second case, we're decreasing by 20% of 50.) The effect
of `40 RET 50 b %` is to compute (50-40)/40, converting
the answer to percentage form as if by `c %`.

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