What is the actual difference between a four digit and six digit grid reference?

A 6-figure grid reference contains 6 numbers which gives us an even more precise location inside the box given by the 4-figure number. ... The third number represents how many tenths you need to move east from the easting value. In our 6-number example, our third number is 4, which represents four-tenths more to the east.

no sé si entiendes español pero te daría la respuesta si lo supiera, pero lo siento mucho