Why does the screen on my laptop expand and shrink at random?

Q  I have a Samsung X420 laptop running Windows 7. It works fine most of the time but sometimes, whatever I’m working on suddenly expands or shrinks in size. This happens in Microsoft Word, Internet Explorer and pretty much every other application window, so I don’t think a particular program is to blame.

Oddly, though, it doesn’t occur when I connect a USB keyboard and mouse and use those to control the PC. Any ideas?
Scott Caulker

A  Many modern laptop computers have touchpads that are able to interpret multitouch gestures or finger movements made only on certain parts of the input area. The Samsung X420 offers both facilities – and we believe this is behind the behaviour you’re experiencing.

In particular, the touchpad on the X420 offers a ‘pinch-to-zoom’ gesture, that works in much the same as many a touchscreen smartphone: placing two fingers on the touchpad and moving them apart has the effect of issuing the open application’s zoom-in function, while moving two fingers together zooms out.

When using the external keyboard and mouse, your fingers and hands are unlikely ever to make contact with the touchpad. However, when using the laptop directly, you’ll obviously be using the touchpad regularly.

Even when you’re not, the palms of your hands will hover nearby or even rest on its surface. It takes only a slight movement across the touchpad to execute commands, so we think this is what’s happening.

If it’s not comfortable to change the way your forearms are angled across the keyboard when using the laptop, then consider disabling some or all of the touchpad’s input gestures.

To do this, click Start followed by Control Panel then click the Hardware and Sound link followed by Mouse. In the Mouse Properties dialogue box you should see a Device Settings tab – click it. Now select the touchpad from the Devices list and click Settings. Use the options listed in the Select an item list on the left to modify the way the touchpad works.

To disable the suspected pinch-to-zoom feature, for example, click Pinch Zoom then click to remove the tick from the Enable Pinch Zoom box. Or click Pointing followed by Sensitivity then PalmCheck to adjust the touchpad’s sensitivity to unintentional input.