Currency conversion slide rule unit

摘要

The slide rule unit has a rectangular sleeve formed from a sheet of carton material that is folded and sealed along one edge 9 and has one open end 13. One side has three rectangular windows 14a,b,c with logarithmic scales relating to currency values.A slide panel is inserted into the sleeve and this has three logarithmic scales. The slide is moved until a specific value relating to one is positioned at a reference location and the equivalent value in a second currency is read off the sleeve scale