Budget fields are available for many forecasting and actual comparison. Variance calculations can be enabled and optionally defined as to which specific variances should be available for reports on projects and tasks.
"Variance Calculation Fields for Projects" and "Variance Calculation Fields for Tasks" work identically for changing these options. Every available variance is available by default so any report user with budget reporting access can choose any available variance.
To simplify if all of these selections are considered overwhelming, click on either link and use the multi-select options to choose only those which should be available for your reports.