Early Canadian Parcel Post Insurance Rate Question

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.

The four tier insurance (3/6/12/30 for up to 5/25/50/100) came into effect 1 October 1921 (when the registration of parcel post was discontinued.)

Source: Monthly supplements to the postal guides, September 1921.

Jan

Added: The postal guides seem to imply that this was the introduction of insurance on parcel post. The insurance was intended to replace registration.

Thank you for that date.

Yes, once insurance became available registration was disallowed. While that held true for domestic parcel post matter. It was not until 1-1-23 that Canada stopped accepting registration for international parcel post. It was that date that the USA and Canada each prohibited acceptance of registered parcel post matter from the other country and allow such parcel post matter to be insured to the other country. As far as I am aware they were the two first such countries with such a mutual agreement. I cannot speak to Canada and other UPU countries other than Canada except Canada no longer accepted registered parcel post from foreign points of mailing for registered handling within Canada. tries.It was later that insured service slow began the spread among UPU countries.

Now to the point of my post, I can now say the service period this calculator was accurate was from 1-1-1921 through 9-30-1921. That is a rather nice short window.