>> However, self-illuminated characters (as on an LCD) do not appear to be >> addressed by that standard and I cannot put my hands on anything >> immediately. >> >> Something that springs to mind immediately is that '15 minutes of arc' >> is a well known (in the human factors community) size for characters.
As I suspected, self-illuminated characters are treated differently. This is because such displays are harder to read than painted characters. I found a reference to 20 minutes of arc. If the person doing this is an imperial only person then it is likely that they also used an outdated 26 inch viewing distance (metric standards are often in the range 600 mm to 750 mm). This works out at 0.15 inch. Did they give tolerances? Engineering specifications get reviewed by many other engineers. There are usually plenty of engineers around who can critique the work of colleagues. Phone calls from the contracts office can usually get resolved quickly by any one of several people. However, user interface work is a rare specialism that is usually done by one person, sometimes a consultant on a short contract. An anomaly in that area of responsibility can therefore go unnoticed or unresolved. > I suspect you are giving way too much credit to the author of the RFP. My > guess is that s/he held some text at arm's length and picked something > that was reasonably readable and then measured it with a ruler As you suggest, I am crediting them with some due process even if it is flawed. If the process is as you suggested an 'arms length' measure, then they are not taking the needs of servicemen seriously and ignoring their own data. If they are using outdated recommendations (as the above reverse-engineered scenario suggests), that is also poor quality work. > Why s/he did not convert it to millimeters is another question. There is no logical explanation for why it is in imperial units. That appears to go against US military policy. I would want to know more about the application before being definitive. However, metric display specifications in other NATO countries are only precise to the nearest 0.5 mm and occasionally the nearest 0.25 mm. A size of 3.5 mm or 4 mm would have been less surprising. -- Terry Simpson Human Factors Consultant [EMAIL PROTECTED] www.connected-systems.com Phone: +44 7850 511794
