Log Units?

[Mark Kampe]

On 04/28/13 13:09, Dirk Hohndel wrote:

> No - the SI units are there for a reason. They make sense to the vast majority
> of the planet (outside such forward thinking countries like Liberia, Birma and…
> I keep forgetting the third one in the triumvirate of brilliance that's imperial
> measurements),

I will make no excuses the stubborn resistance of the US Congress to
the the adoption of a more rational system of measure.  All nations,
and political systems are subject to fits of insanity.  But the most
important person to whom a log entry must make sense is the diver in
question.

Weights labelled in pounds, like (also inferior) yoke valves, are
to be found all over the world ... so while the SI may well be used
throughout (most of) the civilized world, the calibration of dive
weights in kilograms is not (yet).  Presenting information in the
form most natural to each user is just good user interface.

> they allow us to avoid rounding errors (as they are the units
> that we use internally).

I hope I didn't give you the impression I was suggesting a change
in internal units.  The rounding in the conversion from pounds to
grams is already (very explicitly) happening on input:

>       case LBS:
>            weight->grams = val.fp * 453.6 + 0.5;

My weights are labelled in pounds, and that is how weights are
entered for each new dive.  Whether that conversion is done once
upon initial entry, or repeatedly every time the log is read in
should have no computational consequences.

The argument for (my suggestion of) symmetric rounding on the
output side is weaker.  It is more likely to be correct in the
common cases, but could result in round-down if somebody actually
entered small fractional pounds.  But this invites a question about
the importance of precision in this particular metric ... as
(a) lead weights are not precisely calibrated
(b) such precision would be orders-of-magnitude dwarfed by tidal
     lung volume changes.

> And most importantly they are well defined. A "pound"
> and a "gallon" are actually different amounts, depending where in the world
> you are.

The above code would seem to already ignore that complication, and
assume that whenever pounds are entered, they are US pounds.