This has been a long standing issue. We've also had two other issues with slot callouts in the drawing interface. 1) The precision for secondary dual dimension Callout Value (Slot Width/Slot Length) changes both secondary precision (# of decimals). we would like the ability to have three[two] decimal precision on width and two[one] decimal precision on length. 2) The callout arrow flips position when changing precision values. The manual work around is to toggle on "arc extension line or opposite side" under the Leaders tab.