The nomograph is used to calculate distance-time-speed problems. (in the case of navigational problems and these games. A 'nomograph' or 'nomogram'
(wiki) is actually a generic name of graphical tools to calculate mathematical relationships by drawing simple lines)
Draw a diagonal line across all 3 of the nomograph scales. Drag the ends to make it intercept any 2 known scales out of 3 (time, distance or speed). The other unknown value that satisfies distance=speed*time is crossed by the line at the proper mark also. You must know 2 of the 3, or else it's useless.
I don't know how the nomograph looks in SH5 exactly, so I cannot help in what units it displays. If somebody can point me to an image I can help further.