Scrolling

If a text is too big for the screen then the user wants a scroll function so that he can choose which part of the text to see.

There are several ways to do this:

Scrollbar

This is a graphical interface that the user can move with the mouse, as shown to the right. The user can click on the arrow icons to scroll one unit up or down.  The user can click on the shaded field to scroll a half or a full page up or down.  And the user can drag the square button up and down to position the page exactly where he wants it. Simple observations show that most users use the most tedious of all methods: clicking the arrow keys repeatedly until the page is positioned as desired.

Scroll wheel

Some modern mice have a thumbwheel that you can use for scrolling. This is useful for situations where you use the mouse anyway, such as Internet surfing. The scroll wheel is most useful for scrolling small distances. It is not suited for scrolling several pages down.

 

Keyboard

If the user's hands are on the keyboard, then it is certainly most practical to use the keyboard for scrolling. Many systems only have a PageUp and a PageDown key for scrolling a whole page or frame up and down. It is absolutely incomprehensible to me why not all systems also have keys for scrolling a single unit (one line or character) up, down, left, and right, as these operations are needed all the time . This could easily be implemented in existing systems by using key combinations such as Alt+Arrowkey. Without scroll keys the user has to use the arrow keys to move the cursor beyond the edge of the screen window, or use the mouse. (Historical note: The ScrollLock key that all PCs have was originally intended for turning the arrow keys into a scroll mode. Because of the usability problems with modes, this key has almost never been used. If it had been designed as a shift key rather than a mode key, then it would be used by everybody today!)

What is up and down?

What does it mean to scroll up? You have probably never thought of this as a problem, but there are actually two opposite definitions:

1. To scroll up means to move the text up relative to the viewing window, so that the text further down becomes visible.
2. To scroll up means to move the viewing window up relative to the text, so that the text further up becomes visible.

Usability experiments have shown clearly that the second definition should be used. Pressing or clicking an up button or moving a scrollbar or scrollwheel up should actually move the text down relative to the viewing window, so that the text further up becomes visible.

This page was last modified 2008-Dec-08