Fraction is an experimental fraction library for the Arduino. The code is working with a number of limitations among others:

• denominator is max 4 digits to keep code for multiply and divide simple
• therefore not all fractions are exact
• the range of numbers supported is limited.

That said, the library is useful e.g. to display float numbers as a fraction. From programming point of view the fractionize function, converting a double into a fraction is a nice programming problem, fast with a minimal error.

In short, use fractions with care otherwise your sketch might get broken ;)