scale conversion

I hesitate to use the length of a ship for scaling. There are just too many different ones.

Waterline, overall, or deck. With a lot of differences between them.

I use the beam, which on a ship like the Atlantis is pretty simple to determine as opposed to a small sailing ship. In other words her sides are pretty straight up and down, the deck width is pretty much the waterline width/ beam. 

One small problem there is that with smaller number, the division to get the scale factor can be a little fudgy. But this isn't a high accuracy exercise.

Hmm

 I do this a lot . Most of my paper ( card ) models are used as patterns for plastic conversions . The lady that does this for me , knows the math . I do it this way so I have the 1/350 and the original and the original is unharmed .

 Using the paper model is an excellent way to get waterline models all in one scale for a "fleet shelf " . All constant and completely different from Any plastic model . Just remember you better have a great parts box .

For those who aren't up to speed with maths, (like me), I use Frank Krenshaws' Scalecalc 2.5, as discussed here: http://cs.finescale.com/fsm/modeling_subjects/f/2/p/75512/745686.aspx#745686

1/400 to 1/350 is a 114.3% enlargement, (set your /graphics program/printer/copier to 114.3% enlargement)

To get a repeat printable from a scan, I 'print' the existing graphic to an output PDF file, using the print out options eg 114.3% enlargement.

Therafter I use the abobe output.pdf file at 100% print in future.

in RFW's example, 10 5/8", & 1 1/4" is decimal 10.625" & 1.25" (online fraction converter used)

10.625 inches vs. 155 Metres gives a Ratio of 574.34:1

1.25" vs. 18.7M gives a ratio of 588.98:1 .... ho.hum... the perils of working with very small pics.

If you haven't already chopped up the JSC paper model book, I'd scan that & reprint in 1/350, as the parts are more likely to fit...