The unknowns as specified in this record are set to a value specified in the control_unknown_reset_value record (with the same index). By example, unknown_0 is -eptxx, etc.
As a special option you can use -all to reset all unknowns.
As a typical example, you can set strains to zero in a geotechnical calculation, with an -updated material description, after the gravity load has been applied. In this way the strains for further deformations can de distinguished more clearly.