This is a good example, as it retains its original Morocco leather cover and instructions. Most extant examples have lost these. The two moving circular scales are either side of a heavy card tablet. The morocco edging has gilt tooled decoration. The Time Telegraph is simply a non-logarithmic scale for calculating days or weeks between two dates. Palmer’s Computing Scale (improved by Fuller) is a highly accurate circular logarithmic slide rule.
This version of the calculator is for the European market. The computing scale has a page of instructions in French, one in English, and a page of testimonials in English.
Design registration or patent dates 1843, 1845, 1847. Testimonial dated 1848.
Condition: Small losses and wear to Morocco leather. Some discolouration to scales. Both scales still rotate. The finger-holes to operate them have lost their lining. Browning and water stain to instructions.