Conversion Calculators on the Internet?

I have been doing a little checking on some of the new conversion calculators floating around the net, and quite frankly I'm a little disturbed.

Along with the Internet are thought to be some great minds because of some fancy programs they produce. A word of CAUTION would be wise.

It's easy to check the conversion calculators out by using some simple known factors and putting them in. For example: 25.4 mm = 1 inch, 1 std. atmosphere = 760 mmHg @ 0 C and 1 mi. = 1.609344 Km. You see these are absolute numbers; they are not rounded off.

Now, if you were to take the reciprocals of these numbers to 15 places the results would be negligible in most applications, improving over all results. An even better method is dimensional analysis.

It would serve some to learn dimensional analysis. It teaches the fundamental basics of converting from one system to another. Going from the known to the unknown using the lowest common denominators.

One other observation I made is most of the conversion calculators are generated using tables that were not accurate when they were written and are not accurate today. "Numbers rounded off or truncated and some had type-O's". It had to be type-O's, they were never wrong!!!

My conclusion is check them out before you use them. They may save time, but your product will suffer. Oh by the way, I have added a list of Conversion Factors to the PMEL web site.

Ernest J. Huffine (Ernie)
Ernie@PMEL.org

PS: Bad examples in the one I most recently checked.

1 std atmosphere = 76.00021001785151 cm Hg @ 0 C

1 mile = 1.609347 Km

1 mile = 5280.009842519685 ft.

And the list went on.