Both, the Maya numeral system and decimal numbers are positional or place-value notations.
There are two major differences:
1. In the decimal system each numeric position has a value that is a power of 10, whereas in the Mays numeral system each numeric position has a value that has a power 20.
2. In the decimal system place values increase from right to left, whereas in the Maya numeral system place values increase from the bottom to the top.
This app simultaneously displays user generated Maya numbers and their equivalent decimal values at each place value, as well as the final decimal equivalencies for Maya numbers 1 to 1,279,999,999.