# Re: exponentiation of Duration's

```Am 17.11.2010 12:55, schrieb Richard Hainsworth:
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```On 11/17/10 14:03, Moritz Lenz wrote:
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```Am 17.11.2010 10:31, schrieb Kris Shannon:
```
```\$duration * \$duration # WRONG, durations aren't geometric
\$duration * 2 # ok, a duration twice as long
2 * \$duration # same```
```
```
```
http://perlgeek.de/blog-en/perl-6/real-world-strikes-back.html

```
```Ignoring the sarcasm, Moritz's blog and reply seem reasonable about what
should be defined by perl.
```
```
```
Please note that my sarcasm applied only to one particular sentence, not to the whole mail :-)
```
```
```Once a number has been generated, viz., by obtaining a duration, that
number can be manipulated however necessary. The interpretation of the
number is a matter for the programmer, not the language designer.

To illustrate, lets take a different problem. Suppose we have lengths in
\$x and \$y, then the dimension of \$a = \$x * \$y is of area, not of length.
Is it really consistent to forbid \$x = \$x * \$y in case the \$x may be
mistakenly interpretted as a length and not an area?

In the same vein, \$duration * \$duration has the physical dimension of
duration squared. True that is not the dimension of duration, and so
assigning it to a duration variable might cause a problem of physical
interpretation.
```
```
Indeed.

Just as a data point, in physics duration squared does exist.

```
Just think of the definition of acceleration, which is the second time derivative of position. Approximation of derivative as a finite fraction makes it a = x / t^2.
```(And I might add that it also appears in force, energy and power that way).

```
```Neverthless, it doesn't seem to me that trapping dimension errors is
something a programming language should be doing.
```
```
Thank you for phrasing it much better than I managed to.

Cheers,
Moritz
```