keystroking/ keypressing P pointing with a mouse to a target H homing the hand on the keyboard D drawing a line segment on a grid One mental operator M that stands for the time a user has to mentally prepare themselves to do an action, and a system response operator R in with the user has to wait for the system. Execution time is the sum of the times spent executing the different operator types: Texecute = TK + TP + TH + TD + TM + TR. Each of these operators has an estimate of execution time, either a single value or a parameterized estimate. Touch Level Model (TLM) GOMS and it variants were designed for keyboard interfaces, nowadays a new type of interface is omnipresent. This addition to the GOMS family, together with updates to the existing KLM operators, is called the Touch Level Model (TLM). Andrew D. Rice and Jonathan W. Lartigue propose this model for the used to model human task performance on a constrained input touchscreen device and, with proper benchmarking, accurately predict actual user performance. The goal is to provide an instrument for quantitative analysis of touchscreen interfaces. A number of operators are added for touchscreen interactions: Distraction (X) a multiplicative operator that is applied to other operators to model real world distractions Gesture (G) gestures are conceptualized as specialized combinations of finger movements across the device's screen Pinch (P) refers to the common two-finger gesture Zoom (Z) the reverse application of the Pinch operator. value in MS = 200 Ms Initial Act (I) KLM assumed the user is prepared to begin an action, touchscreen devices require users to prepare them for use (home button or password) Tap (T) operator refers to the physical action of tapping an area on the touchscreen device in order to initiate some change or action Swipe (S) usually a horizontally or vertically swipe like changing the page in a book. value in MS = 70 Ms Tilt (L(d)) used with an interacting with a devices equipped with accelerometers. Rotate (O(d)) gesture in which two or more fingers are placed on the screen and then rotated about a central point Drag (D) similar to Swipe, Drag also involves tapping a location on the screen and then moving one or more fingers in specific direction CMN-GOMS CMN-GOMS is the original GOMS model proposed by Stuart Card, Thomas P. Moran and