The system used in this calculator is a base 20 number system in which the individual digits are written vertically (from highest weight at the top, to lowest weight at the bottom).
This is what the digits used in the Mayan number system look like:
Article based on which the converter was made: (link: Wikipedia)
Picture used as an icon: (link: maxpixel.net), work licensed under CC0 Public Domain
Picture showing Mayan numerals: (link: Wikipedia), author Bryan Derksen, work licensed under CC BY-SA 3.0