Used to produce an epoxide of certain stereochemistry

OCC([1*])=C([2*])[3*]

becomes with addition of (+)-DET and

OC[C@]1([1*])O[C@@]1([2*])[3*]

where the epoxide oxygen is meant to stick into the screen

Mnemonic

Left hand rule
Thumb =
Four fingers = alkene
Negative (-) = kNuckle
Positive (+) = Palm

This mnemonic was developed by Professor Hung Pham in grad school.