Answer:
The instrument is used in mechanical drawing. it is, as the name suggests used to draw curves mechanically, as opposed to free hand. Unlike slide rules, French Curves are not obsolete and are still manufactured. Good art-supply houses in New York can fetch you up with a Koh-I-Noor, named after the famous diamond . Koh-I-Noor used to make slide rules, but not anymore, they do make drafting instruments. Your Fren ch curve may be identical to one used on the Chart table of the (France) or on the Navigator"s board on the Concorde, history in the making. they are (Manufrance) made in France so naturally got the nod on merchant and defense contracts. Yes, as I have suggested they are useful in cartography- map making and charting- including Weather maps with temperature curves, etc. Buy one! By rthge way Koh-I-Noor means Mountain Of Light in Arabic. Noor- name of the Jordanian Queen roughly translates as (Lucy) again from Lucia- Light. Lucid-clear, etc. back to the drawing board with Diamond quality.