A small cube is 1. We call it a unit.
- Ten units in a row make a rod: 10.
- Ten rods side by side make a flat: 100.
- Ten flats stacked up make a big cube: 1,000.

To read the blocks, count each kind and add them up. 2 flats, 4 rods and 3 units are 200 + 40 + 3 = 243.