There are a few ways to enlarge the text displayed on the iPhone. Each method is useful in different situations. You may already be aware of some of these options, but I’ll bet you don’t know all of them.

• When viewing web pages using Safari or email messages, you can spread your fingers to enlarge the text size. The “Pinch Apart” gesture entails placing two fingers on the iPhone screen and then sliding them apart from each other. To reduce the size of text, you pinch your two fingers back together. For more details on how to execute these gestures check out this helpful web page on gestures.

The next two options require an iPhone 3GS or newer.

• Turn on the Zoom function. You can enable this feature by opening the Settings app, selecting General, then Accessibility.  Finally, tap on Zoom and turn it on. Zoom magnifies the entire screen whenever you double-tap the screen with three fingers. Double-taping with three fingers a second time turns off the zoom function. You can move around the screen by pressing three fingers on the screen and dragging them around.

• Turn on the Large Text function. You can enable this feature by opening the Settings app, selecting General, then Accessibility.  Finally, tap on Large Text and select a text size. This feature makes text larger in the following applications:  Calendar, Contacts, Mail, Messages and Notes.

I should mention that the iPhone actually includes a great number of features that enhance usability and accessibility for people with limited vision, hearing or other impairments. Apple describes them all on their web site.

Here are some simple instructions on how to enlarge the size of text on a web page when you’re using Safari, Firefox or Chrome on a Macintosh computer. I use this feature on a daily basis since web sites use a variety of font sizes. This is especially handy in low-light settings or if one typically needs glasses but they aren’t handy.

All three of these web browsers support the same keyboard shortcut. While viewing a web page, press Command + (plus sign) to enlarge the text size and Command – (minus sign) to reduce the text size. If you prefer to use menu commands then go to the View menu and select Zoom In to make the text size larger or Zoom Out to reduce the text size.

Update March 2013: Added instructions for OX 10.8, Mountain Lion.

Did you know that Mac OS X has a built-in zoom feature? This feature lets you zoom in on your screen so everything on the screen is larger. Of course, when you zoom in you can only see part of the screen on your monitor. You’ll need to scroll around to see the other parts of the screen.

I use the zoom feature frequently when I’m giving presentations especially when I provide Mac training. I project my Mac laptop’s image onto a wall or screen using a projector. Then when I want to show audience members something on the screen, I zoom the screen so that everybody in the audience can see what I’m trying to highlight on one part of the screen.

Zoom is off by default. For Mac OS X 10.4-10.7, follow these instructions to turn it on:

• Go to the Apple menu and select System Preferences.
• Click on the Universal Access icon.
• Click on the Seeing button.
• In the Zoom section set the button to On.
• Optionally, click the Options button and make sure in the section titled “When zoomed in, the screen image moves:” that it is set to “Only when the pointer reaches an edge”. Click Done. The other options lead to too much screen movement which I find distracting or even annoying.

For Mac OS X 10.8, follow these instructions:

• Go to the Apple menu and select System Preferences.
• Click on the Accessibility icon.
• Click on Zooming in the left-hand column.
• Check the box “Use keyboard shortcuts to zoom.”
• Check the box next to “Use scroll gesture with modifier keys to zoom.”
• Optionally, click the More Options button and make sure in the section titled “When zoomed in, the screen image moves:” that it is set to “Only when the pointer reaches an edge.” Click Done. The other options lead to too much screen movement, which I find distracting or even annoying.

Once the zoom feature is enabled then you can invoke it at any time to zoom in on your Mac’s screen by simultaneously pressing these 3 keys: Command, Option and the Plus Sign (which is typically the same as the Equal Sign key). Each time you press these three keys your Mac will zoom in a little bit more.

To zoom out simultaneously press these 3 keys: Command, Option and the Minus Sign key which is typically to the left of the Plus Sign key.