I am trying to determine the period of validity for an early Canadian Parcel Post Rate Calculator I have. While shown in the images, what makes this especially unusual is how it was produced. The outer wrapping is a heavy card-stock with a heavy coating of ink. The interior slide is enameled on tin. If one reads the advertising, it is no surprise as the company was in business to enamel tin. And, what better way to demonstrate your company's ware than giving away a quite useful sample?
Insurance began 1-1-1921 with a two tier system, $25/$50; 5/10 cents and as of 1-1-1923 when international insured parcel post began between the Canada and the USA, the Canadian insurance was four tiers, $10/$25/$50/$100; 3/6/12/30 cents.
When did either the two tiers drop in cost or when did the two tiers expand to more than two tiers on or before 1-1-1923?
That information gives me the end date of the "correct period of use" for this calculator.