Answer the questions in the problems below. Hand in your answers on one sheet of paper (8.5" x 11"). You may, but need not, use both sides of the paper. Papers longer than this limit will be truncated to one page before marking.

This is an individual exercise, i.e. the work you hand in must be the results of your own efforts. Turn in your solutions at the beginning of class on September 30 Monday.

1. Visual angle (15 %)

The resolution of human eyesight is usually measured in cycles per degree of angular width or height. It is often useful to be able to estimate roughly the visual angle subtended by an image or object. One way to do this is to hold up one of your thumbs at arm's length and compare the angular width of the object with that of your thumb. In this exercise, you are to "calibrate" this "measuring instrument" by determining the visual angle subtended by your thumb held at arm's length and then to estimate the angular width of the moon.

1. Determine the angle subtended by your thumb at your arm's length by (1) measuring the width of your thumb, (2) holding your thumb at arm's length and measuring the distance between your eye and your thumb, and then (3) calculating the angle.
2. Estimate the angle subtended by the moon by comparing it with your thumb held at arm's length. Do this immediately; do not wait until the day before this assignment is due, as the sky might be cloudy then.

An LCD computer screen is about 30.5 cm wide and 22.9 cm high and displays 1400 by 1050 pixels. The viewer's eyes are about 50 cm from the screen.

1. Calculate the number of pixels per degree of visual angle as seen by the viewer.
2. What is the maximum resolution (in cycles per degree as seen by the human viewer) of an image (e.g. a pattern of bars) displayed on this screen? Remember that two pixels (one light and one dark) are required per cycle.

You are working for a company currently engaged in the preliminary planning and design of a system which is to provide telephone and short text message services to hand held devices anywhere on earth. You are in a small group planning the data entry part of the hand held device, with which both alphabetic information and digits will be entered. The size of the hand held unit will be about 6 x 15 x 3 cm. Even a small finger driven mechanical keyboard would be too large, so a tentative decision has been made in favor of a combined display and touch screen activated by a small stylus. The main question now of concern is what layout of the letters and digits should be selected. The list of alternatives has been shortened to three: (1) the standard typewriter keyboard layout, (2) a layout in alphabetic and numerical order and (3) another (unfamiliar and apparently random) layout which has been shown to permit very fast input when the human user has been trained in its use. With alternative 3, trained users can achieve speeds several times faster than with either of the other alternatives, but alternative 3 requires training and drill lasting several days to achieve even moderate proficiency.

1. Which HCI design goals are particularly relevant in this case? I.e. which factors should be considered when trying to optimize the design?
2. What kinds of users would you expect to predominate (novice, occasional, etc.)? What would you expect to be important to the users (what are their requirements)? Which of their requirements vary significantly from one user group to another? Consider both the nature of the tasks (entering telephone numbers and text to be transmitted), the usage environment and the physical size of the device.
3. How important are the design factors you identified in question A above in view of the requirements you identified in B above?
4. What data entry scheme would you recommend to your company? Why? (You need not restrict yourself to the three alternatives above, but if you select another, justify it convincingly.)
5. What form of feedback to the user would you recommend? not recommend? Why? If optical, where should the feedback be presented to the user?