# Learn@UW/D2L - Constants pi and e Must be in Lower Case in Formula Calculation Questions

The constants **pi** and **e** must be in lower case in the formula in Arithmetic and Significant Figures questions that may be used in quizzes.

If you test a formula containing **PI** or **E** using the "Test" button, the symptom is the message

"Error: Input string was not in a correct format."

Existing quiz questions using upper case **PI** or **E** in the formula may not be properly scored.
You should edit such questions changing **PI** to **pi** and **E** to **e**.

In previous versions of the Learn@UW application, upper case **PI** and **E** were allowed.

This is a known issue.