# Scale selection tool for modellers - (follows from 'Scales and real-thing equivalence' thread)

http://www.nearingzero.net/ss.html
It's based on three variables, not in this order:
1. How long or wide the real subject is (easy).
2. How far you'll be viewing the model from when drinking beer, e.g. with magnifying glass, at arm's length, in a display cabinet, hanging from the ceiling, in the hand of a happy looking child in the garden next-door...
3. How much of your field-of-vision you want to fill. This might be the hardest thing to figure out. However, an ideal viewing arc that's assumed for setting up a home TV system is 30 degrees of your total 180 degree f.o.v. I think this is angle is big enough to keep your attention by filling a reasonable amount of your visual field (about 17% of the total). The ability to compete for a reasonable arc of the visual field probably also accounts for the "show-stopper" effect of the bigger scales. This angle of 30 degrees is set as the default viewing arc, but can be changed by the user.
The output is selected from seven common scales: 24th, 32nd, 48th, 72nd, 144th, 350th and 700th, according to which is nearest. (Other scales are ignored at the moment -- Excel only allows up to seven nested IF functions in the one equation.).
It can also be used backwards, by changing the viewing distance until the actual scale is reached; e.g. it will tell you that to view a 1/72nd scale XB-70 Valkyrie lengthwise at a 30 degree arc, you have to be 5 feet away. The original is about 60 metres (200 ft) long. The view the single remaining XB-70 at the same arc, you have to be about 120 yards away (which may not be possible...). This could possibly be useful for un-zoomed photos, but bear in mind that a camera already starts off with a cropped visual field (of much less than 180 degrees).
This is just a tool --- it won't necessarily suit someone who'd prefer to work to a constant scale. However, I think the output probably supports comments made by modellers about picking a scale that "just feels right" for the subject.
Regards,
Nick.