Digital Representation-with references

The digital representation of information often involves a tradeoff between the amount of storage required and the precision of the representation. Some kinds of information have no exact digital representation.

Identify one type of information that is typically given an approximate digital representation. Briefly explain why this is the case. What are the common approximations, and how close are they? In what situations is this approximation a problem?

In about 1 page, answer the above questions, and please cite your work. I need the references!