Welcome to the Forum! One of the most useful tools a modeler can buy is a pocket calculator that works in feet, inches, and fractions of an inch. If it also converts between the English and metric systems, that's even better.
Such calculators used to be rare and expensive, but in the past few years they've become standard merchandise at hardware stores and "home centers," like Lowe's and Home Depot. If you have trouble finding one locally, try the Lowe's website ( www.lowes.com ).
Several levels of sophistication are available, but for model building the simplest probably will do. (You probably don't need to solve rafter slope problems, or estimate prices in terms of cubic yards of concrete.) A perfectly satisfactory calculator for model building can be had for less than $20.00.
To use the thing is simple. Say you're building a 1/72 scale model, and the plans you have in front of you are on 1/32 scale. From the chart in the post above, you know the conversion factor is .44444. So, using a ruler, take whatever measurement you like on the drawing. Enter it into the calculator - in feet and inches (assuming the drawing is in the English system). Divide that number by .44444. The calculator will give you the answer, to the nearest 1/64".
If the drawing was made with the English system and you prefer to go metric, go through those steps and hit the conversion key. The calculator will give you the answer in milimeters.
Believe me, this is a good way to spend twenty bucks.
Youth, talent, hard work, and enthusiasm are no match for old age and treachery.