A Systematic Review of Modifications and Validation Methods for the Extension of the Keystroke-Level Model

Table 2

Heuristic rules for M operator placement [6].

Rule 0	Insert Ms in front of all Ks that are not part of an argument string. Place Ms in front of all Ps that select commands.
Rule 1	When an operator following an M is fully anticipated in the operator just prior to M, remove the M.
Rule 2	When a string of MKs belongs to a cognitive unit, delete all Ms except the first.
Rule 3	When a K is a redundant terminator, delete the M prior to the K.
Rule 4	When a K terminates a constant string, delete the M prior to the K; however, do not delete the M when the K terminates a variable string.