Why do some signs look the same?

It was not always obvious which number is meant when looking at cuneiform.

For example, the sign could be used to represent 1 or 60.

This sign could represent these different values:   2 or 61 or 3601

However, the scribes sometimes left spaces between the signs to show which value was meant. For example:

the number 2 would be written like this:
but 61 would be written like this:

See a full set of numbers