Website last updated 03 August, 2010

CF/M Scale

The CF/M scale is a C scale folded at ln(10). It's found on the slider, and its counterpart DF/M is found on the stock.

ln(10) is about 2.3, which is not particularly close to the middle of the C scale. Thus, although you can jump up to CF/M, DF/M when your result is offscale at C/D, there are better folded scales for this. Read Tutorial on Folded Scales here.

A better use for DF/M is to read natural logs off of the LL_X scales. If you have LL_E scales, you can read their natural logs on D, but LL_X scales are in base 10. DF/M has the conversion to base e built in so you don't have to do an extra multiply.

If your LL_X scales are on the slider, you would include a CF/M scale, if they're on the stock, include a DF/M scale.

The result is merely the log base 10 value on D multiplied by 2.3. All the other considerations for finding logs and exponents with the LL scales apply.

The CFM/DFM pair are the equivalent logarithm converters in the case of a slide rule with LL_E scales.