HTC one s User Manual page 23

23 Your first week with your new phone
Slide with two fingers
Two-finger swipe
In some apps that have sorting, like Mail or Contacts, swipe up or
down using two fingers to scroll the screen. The screen displays the
sorting order, and you can easily scroll to the information you want.
In some apps, like Gallery, Messages, Mail,
or the web browser, slide two fingers
apart to zoom in when viewing a picture
or text.
Slide two fingers together to zoom out of the picture or
text.