While Li and Holleis both agree that the KLM model can be applied to predict task times on mobile devices, Li suggests further modifications to the model, by introducing a new concept called operator blocks. These are defined as "the sequence of operators that can be used with high repeatability by analyst of the extended KLM.”. He also discards old operators and defines 5 new mental operators and 9 new physical operators, while 4 of the physical operators focus on pen-based operations.