Try this chaps and chapesses, this is what I specify and have specified over the last ten years.
Character Size. Numbers, letters and symbols associated in a datablock shall be of such a size that they are clearly readable from the controller's normal operating position at the console. It is recommended that the minimum size should be 4mm.
The minimum size of the characters should correspond to the following formula:
Character Height = Viewing Distance in mm X 0.0002908 mm / minute of arc. .Where; Character Height = 20' of arc. .Character width = 70% of height. .Stroke Width = 12% of height. .Space between characters = 20% of width. .Space between rows = 30% of height (radar label only). .(For continuous lines of text the row space = 60% of height minimum)
What is so important about the size of the window? When it is "see through" and "control through", there is no real problem as it becomes relatively unimportant. The font size remains important though.
All the best in NERC, I was doing my bit in the 80's but nobody would listen. <img src="smile.gif" border="0"> <img src="smile.gif" border="0">