How do I create a deduction on a current timesheet?

Deductions can be created by adding in another Rate Code line to the timesheet. On this line the amount will be entered as a negative, in order to represent the deduction.

A deduction like this can be done at the validation stages (via Timesheet Validation or Incoming Timesheet Images) or post validation from the Timesheet Display Option:

In the example shown above a Rate Code Entry has been set up with a description of Adjustment - you may want to create a new Rate Code Entry yourself to suit the description of the adjustment you are making.