4. The following is a screen from a spreadsheet program:

The designer of the program has observed users using a method to locate a cell on, or to the right of, the current screen that involves clicking in the scroll bar to the right of the position indicator box (see diagram) at the bottom of the screen 0 or more times to get to the target screen, then clicking the mouse after moving the pointer to the required cell.
The designer wishes to introduce a "Goto cell" command, which is invoked by selecting "Goto cell" from the "Go" menu (using the mouse) at which point a dialogue box appears. The user then types the cell reference <letter><number> (e.g. "G7") into a field (which is already selected and ready to receive text) then clicks an "OK" button. The display then changes (if necessary) to the screen containing the target cell, which is automatically selected, resulting in the system being in the same state as that following the first method.
The designer wishes you to determine at which point the "Goto cell " method will become more efficient for a user than the first method. Use a parametric keystroke analysis to help you to perform this analysis. Consider only rightwards movement (i.e. the row of the target cell is within the rows currently displayed).
Briefly discuss whether or not your analysis indicates that the "Goto cell" method would be a useful addition to the system. [20 marks]

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