No matter what type of software you use, it's your computer monitor that enables you to actually see and interact with an application. It's important, therefore, to make sure that your monitor is set up properly. A poorly adjusted monitor will affect the manner in which you work and may even strain your eyes so badly that it could bring on regular headaches if not dealt with properly.

There are, however, a number of display controls provided within Windows - and some equally important additional controls that are built into the monitor itself. Easily overlooked, it's worth knowing how these work so you can make the most of this vital piece of equipment. Here's a bird's eye view of monitor settings to help clear your vision.

Down the tubes
Despite falling prices and the increasing popularity of flat-panel monitors, most computer users still rely on old-fashioned and rather bulky cathode-ray tube (CRT) monitors with their PCs. Like a television set, these monitors are built around a large glass tube.

At the back of the tube is a mechanism that shoots a beam of electrons across the glass panel at the front of the screen. Coated with coloured phosphors that react to the barrage of electrons, the glass panel lights up to create the coloured images you see on a screen.

CRT monitors are cheaper and more common than flat-panel displays, and they also tend to have more control options so we'll concentrate on them for now.

Right on the button
The first thing you need to do is locate the various buttons and dials that allow you to control your monitor. That's easy enough, as they're generally mounted on the front of the monitor. Figuring out exactly how they work can be a bit more complicated.

The ones you'll notice first will probably be the brightness and contrast controls. These are the two main options that actually affect the visibility of the image on your screen, and most manufacturers are sensible enough to provide clearly marked controls, along with further buttons that allow you to increase or decrease these settings.

Try out a variety of brightness and contrast settings and see which feels most comfortable: if you find your eyes ache after a day's computing, try lowering the brightness setting or increasing the contrast.

Peruse the menu
These basic controls merely scratch the surface of mastering your monitor's output. Adjusting the brightness and contrast might not be as simple as pressing one or other button. Most modern monitors include a button that fires up an on-screen display (OSD). This is a menu that appears on the screen and contains a comprehensive set of controls.

It's important to realise that an OSD menu is something that is built into the monitor itself. It has nothing to do with Windows or any other software you are running on your PC, so don't confuse the OSD with the Display Properties control panel that is part of Windows.

If you're lucky, you'll see a button marked 'Menu' on the OSD. Alongside this, there'll be additional navigation buttons that allow you to select and adjust the various options within the menu. Unfortunately, manufacturers tend to make a real mess of this, and some monitors feature indecipherable buttons.

To make matters worse, some buttons can also have more than one function. You'll need to consult the manual supplied with your monitor to figure out exactly how the menu system works but bear with it as the options this gives you to change your display are manifold.

Geometry class
Once you've activated the OSD you'll see a menu containing a number of options. The most important of these are the 'geometry' settings, which control the shape, size and position of the image that you see on screen. You might think that the on-screen image is a simple rectangle with a fixed shape and size, but it's only the glass screen itself that is rectangular. The image 'painted' onto the glass screen by the electron beam inside the monitor can be distorted into all sorts of different shapes and sizes.

The simplest of the geometry controls are for width and height. These allow you to increase or decrease the dimensions of the image so that it completely fills the available screen area (or shrinks down into the middle of the display, should that be your wont).

If the image is too small, you'll see that there's a large black margin of unused screen space around the edges of the Windows Desktop. If it's too big you might lose some items from sight altogether. The My Computer and My Documents icons, for example, tend to sit in the upper-left corner of the screen, and they can get squeezed right off the edge if the image isn't sized properly. Adjusting your monitor's screen height and width controls will bring them back into view.

You should also find related controls for horizontal and vertical position (or 'shift'). The horizontal-shift control allows you to nudge the displayed image to the left or right so you can accurately position it in the centre of the screen. The vertical shift performs a similar function, allowing you to move the image up or down.

You can use the shift controls to get the image centred properly and then adjust the width and height to make sure you really use all of the screen space. Many monitors also include a display-rotation option, which will allow you to rotate the image clockwise or anti-clockwise.

These controls will mainly come in handy when you're setting up a PC for the first time, but you may also find you need them to fine-tune your monitor whenever you switch resolution using the Display Properties control panel in Windows. Switching resolution can cause the image to change size or shape slightly, making it necessary to adjust the image once more.

You could have an auto-adjust (or auto-image) option that attempts to automatically adjust the image for you. These don't always work perfectly so it's worth experimenting with the main geometry controls to find out how to adjust the view yourself. Many monitors also have a small amount of memory built into them, allowing them to store settings for different resolutions.

Some people like to switch their monitor to high-resolutions for detailed graphics work such as photo-editing, and use lower resolutions for more routine tasks such as word-processing. Being able to store different settings in the monitor's memory will enable you to quickly change resolution without having to readjust the monitor each time.

Roll out the barrel
A number of more advanced geometry controls may also be available. These will vary from monitor to monitor, and more expensive monitors aimed at professional designers or photographers may provide some very specialised controls that are useful for high-quality graphics display. The low-cost monitors provided with many home computers tend to be less sophisticated, but even these have a number of additional options, such as 'pincushion' and 'trapezoid' adjustment.

Pincushion distortion (sometimes also called 'barrel' distortion) occurs when the left and right, or top and bottom edges of the image become curved rather than straight. This makes the image look barrel-shaped rather than rectangular. They may become concave (arching inwards) or convex (bulging outwards), and these controls allow you to adjust the edges so they're straight once more.

Trapezoid distortion is what happens when one edge becomes shorter than another, creating a trapezoid-shaped image rather than a nice regular rectangle. Of course, most monitors are tested before they leave the factory, but these sorts of distortions can occur when a monitor is in transit. A bumpy van ride can knock the monitor out of whack so the image is distorted when the monitor is delivered to you. All such problems can be rectified with the geometry controls.

Gassing about degauss
In addition to the geometry controls there are a number of other options that it's useful to know about. One control that often confuses people is the mysterious 'degauss' option.

Many monitors have a specific degauss button, although it may be buried within the depths of the OSD menu. When the Degauss option is selected, the monitor makes a strange rattling noise, and the image shakes for a second or two, before settling down once more.

So what's degauss all about? Well, it's important to remember that the electron gun inside a traditional CRT monitor is a very sensitive piece of equipment, calibrated at manufacture with microscopic accuracy. Its operation can be affected by any nearby electrical equipment - such as other computers in a large office - or even by the earth's magnetic field.

Such influences on the electron gun can cause the image to become distorted. The degauss prompts the monitor to try and de-magnetise itself in order to compensate for magnetic distortion.

The chances are you'll probably never need it, but many people are curious about it purely because it's clearly important enough to warrant its own special button on many monitors.

Temperature control
Other options that are of more practical use are the 'colour temperature' and 'convergence' controls. The screen of a CRT monitor is coated in very fine dots of three different-coloured phosphors - red, green and blue. The colours you see on the screen are created by mixing those three colours to create millions of others.

If those coloured dots aren't accurately aligned, the image on your screen will look blurry. The horizontal and vertical convergence controls provided on some monitors allow you to align the coloured dots more accurately in order to create a sharper image.

The balance and intensity of the different coloured dots is what's known as the 'colour temperature'. Ordinary daylight is said to have a colour temperature of around 5,500 degrees. Lower temperatures produce light with a yellowish hue, while higher temperatures tend to shift towards blue. You may sometimes need to adjust the colour temperature of your monitor in order to compensate for a colour cast that is caused by the lighting in your home or office.

This isn't likely to be a problem for people using a PC at home, as domestic lighting tends to emit fairly plain, white light. But if you're a keen photographer and you understand a bit about the science of photography, you might find that adjusting the colour temperature of your monitor is useful when using image editing software such as Adobe Photoshop. You might also find the colour-temperature controls useful if your workspace is subject to varying lighting conditions throughout the day.

This brings us nicely into the area of colour calibration. In brief, these controls - assuming your monitor has them - enable you to ensure that the images shown on the monitor's screen match those experienced in the real world as closely as possible. For this reason, unless you are a keen image editor, the vast majority of computer users can ignore these controls and leave them to the precise eyes of professional photographers and designers.

Look sharp
The geometry and image controls that we've discussed here should be more than enough to help you master your monitor so that you can make the most of its abilities and work efficiently with a wide range of business, gaming and creative software.

Remember, you can't damage your monitor by experimenting with these controls but not knowing how to address that eyestrain could bring on unneccessary headaches. So don't be afraid to press a few buttons just to see what happens. A poorly adjusted monitor can have far-reaching consequences, so a few minutes taken to explore the controls is well worth the effort.

Flat-panel monitors
As noted earlier, most of us are still using CRT monitors, but flat-panel monitors are becoming far more affordable these days. And, of course, they're a standard part of all notebook computers.

Flat-panel monitors use a completely different technology, known as TFT, to produce the image you see on the screen. Most TFT monitors will have their own OSD menu that allows you to adjust settings such as brightness and contrast. However, because they are not subject to the sorts of distortion that can affect a CRT display, they don't need the same range of geometry controls.

You will never, for example, need to degauss a TFT monitor nor rotate or straighten up the edges of an image. However, horizontal and vertical positioning controls should be available in standalone TFT displays, though not those built into notebook computers.

It's also worth knowing that some flat-panel monitors may have a few extra features of their own. You may have the ability to switch between an analogue video signal or higher-quality digital video signal. Your choice here will depend on the type of graphics card your computer has, so check the card's manual for further information.

You may also find that flat-panel monitors are supplied with special software that provides additional features, such as colour calibration options that will come in handy for digital photography. As always, it's important to check the manual provided with your monitor so that you don't miss any useful features.

Colour and resolution
The choice of resolution and colour depth is controlled not by the monitor, but by the graphics card inside your PC. The graphics card, in turn, is controlled by a driver that should already be on your PC. The driver software options will appear inside the standard Display Properties panel, which you can access by right-clicking anywhere on the Windows Desktop and selecting Properties from the pop-up menu.

Bear in mind that a PC running at a high resolution and colour depth requires a bit more horsepower, as the graphics card has to deal with lots more video data each time it flashes an image onto the screen. Older PCs might slow down a bit when running at 32-bit colour depth. Fortunately, most PCs and graphics cards released in the last few years can handle high-resolution images and colour depth without any strain at all.

There is one crucial setting that you'll find under the Advanced tab of the Display Properties control panel. The refresh rate of the monitor can have a severe effect on the health of your eyes. A low refresh rate - anything lower than 70-72Hz - creates a flickery image that can cause eyestrain. Windows will automatically select the highest refresh rate possible, but it's worth checking the Display Properties settings yourself to ensure that you've chosen a suitable refresh rate.