Dear Markus and All (note K in Markus), Thanks for these ideas. I have, for a long time, used a rule of thumb that says the observing distance of lettering that you want to be readable should be 100 times the height of the letters.
To my mind this allows for readers who have diminished sight due to age, and for those who are not currently wearing their reading glasses. This differs from your calculation "6 mrad large (3 mm capsize at 0.5 m viewing distance)" as my method would produce letters 5�mm high at 500�mm viewing distance. My method has the advantage of being easy to remember and easy to use. For example if you are preparing a poster for a conference where you expect your audience to stand two metres away to read the 'headlines' you would set these at a minimum of 20�mm (2000 � 100 = 20�mm) with the smaller text � to be read at one metre � set at a minimum of 10�mm (1000 � 100 = 10�mm). On a larger scale if you wish to set a billboard in a field 40�metres from a road then you would set the minimum text size at 400�mm (40�000 � 100 = 400�mm). Another aspect to this debate is the issue of the economics of the quantity of writing that you can fit on an expensive small screen. Cheers, Pat Naughtin CAMS Geelong, Australia > This depends on the field of application. I agree that the rad is > unpleasant for common construction angles sich as 90� or 45�. On the > other hand, we had for example in the XFree86 group (the people who > maintain the windowing software used under Linux) recently a discussion > about the mess with font sizes, and there was some agreement that in > screen display and projection applications, users are really more > interested in visual angle rather than absolute character height. Here, > the rad or better the millirad (mrad) is an excellent and highly > convenient unit. 1�mrad is the visual size/angle under which you see a 1 > mm large object at 1 m distance. The font I am currently using to type > this text is 6 mrad large (3 mm capsize at 0.5 m viewing distance), > which I find a very convenient unit. > > While I find the 360� circle perfectly convenient for large angles in > constructuion, I wish that people would use the rad, mrad and �rad more > often for visual angles, especially in optics and astronomy. I find > arcseconds very unintuitive, whereas in order to know what a �rad is, I > just have to think of a microchip bus line in a meter distance or a > millimeter in a kilometer distance. > > Give the radian a chance, it is for small angles the most convenient > unit (resolution of telescopes, aiming spread of guns, etc.).
