Place value cube manipulatives

This is a set of base-ten place value manipulatives: units, rods of 10, flats of 100, and cubes of 1000. The default unit size is 1 cm, the same as for commercially produced sets. You can also create blocks of any dimensions, just in case you find yourself teaching kids [duotrigesimal numbers](https://en.wikipedia.org/wiki/Ngiti_language#unusual_numeral_system).

# Updates

- 2022-02-11 Fixed a bug that left strange notches in some of the grooves.