# 3 questions in 7 dyas.

Assume you have the calculator in the image below. Use Fitt’s law to estimate the time it will take to enter the following key sequence (starting with the finger on top of the “ON” key): 3, 8, “ENTER” (finger hits the top of the first E), 5, , 2, *, √x.
You should use this instantiation of Fitts’ Law: T = C * log2(D/S 0.5) where C = 100ms, each key is 0.3″x0.3″, rows and columns are 0.44″ apart (center to center), and users wait 200ms between keys.NOTE: Even though the keys are obviously spaced differently vertically and horizontally, use the above assumption to simplify your calculation. This HP calculator use the Reverse Polish Notation. The sequence represents SQRT((38 5)*2).
2. (30%) The manufacturer of this device decides to increase the device dimensions by 25% (both directions; size and distance). How will this change the time it takes to perform the sequence above?
3. (20%) The manufacturer decides to increase the distance between each key by 25% (both directions; distance only), but to save money use the exact same key size as in the original device. How will this change the time it takes to perform the sequence above?