All our postcards have a functional nature. They are designed to be able to learn the use of instruments that were in the past essential instruments of daily life, such as the astrolabe, the night labe, the solar clock and the perpetual and lunar calendars. They are made of cardboard and always have a place to write a message to the person to whom it is sent or given.
The set is made up of five postcards for the price indicated and keep in mind that you can also find all of these instruments made of metal in the different sections of our page.
The instructions to learn how to use them, being in some cases very detailed, can be found in different sections of our blog. From there you can download them and if you want to print them for your study.
We have given the postcards the golden number of proportions, that is
the numerical value of the proportion between two line segments a and b (a longer than b), which meet the following relationship:
The total length, sum of the two segments a and b, is to the largest segment a, what this segment a is to the smallest b. Written as an algebraic equation
