One thing stressed at Auburn (1969-1973), in many classes, was "dimensional analysis" aka "conservation of units".  If your units came out right, then
after using your slide rule, the only error could be ... the decimal point. And on a typical 25 point question, the answer being off by a factor of ten
cost may be 2 points (hope this was not a bridge design...).  In the real world you would use a Calcomp calculator or IBM adding machine, or an IBM
360 model 50 computer and run Fortran (Fortran does not know "units" but is great with decimal points).

Anyway while doing a project once, the European process engineer developed a very elaborate spreadsheet that totally modeled the new recycle plant.  One
of the worksheets had nothing but physical constants that could be used over and over.  One constant that was used literally hundreds of times was the density of water.

So I asked the project manager when did we add a chiller to the project?

Off course there was not a chiller in the scope.  The density of water entered was for 40F (cold), rather than 40C (warm - 104F).  

Larry Wells
Atlanta, Georgia USA

****

****

Have a comment? Send your email to jthompson@taii.com. Unless you tell us otherwise, we will assume we can use your name if we publish your letter.