Non-LBFGS jobs:  The criteria for terminating all optimizations, electronic and geometric, are to be increased by a factor, normally 100. This can be used where more precise results are wanted. If the results are going to be used in a FORCE calculation, where the geometry needs to be known quite precisely, then PRECISE is recommended; for small systems the extra cost in CPU time is minimal. PRECISE is not recommended for experienced users; instead, GNORM=n.nn and SCFCRT=n.nn or RELSCF=n.nn are suggested. PRECISE should only rarely be necessary in a FORCE calculation: all it does is remove quartic contamination, which only affects the trivial modes significantly, and is very expensive in CPU time. 

LBFGS jobs: In the LBFGS procedure, if  PRECISE is present then the number of cycles used in identifying the lowest-energy system is increased from 30 to 60. 

See also LET.