RE: let's bump to 10mm from 9mm

Ø  Be sure to check for interference on each axis of a target. To avoid interference errors, make sure that touch targets are at least 8 millimeters apart on center

I’m not confident on the use of “on center” being helpful to us because many users may not be hitting the targets on center and this allows for the actual touch sensitive area of the elements to be very close together without specifying an inactive space between the elements.

Jonathan

Jonathan Avila
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From: David MacDonald [mailto:david100@sympatico.ca]
Sent: Thursday, December 17, 2015 1:33 PM
To: public-mobile-a11y-tf@w3.org; Jan Richards
Subject: let's bump to 10mm from 9mm

I'm thinking we should bump it to 10mm and remove the "one dimension" part. I think we can delete 2.5.4 (or collapse in 2.5.4, 2.5.5), something like this...
2.5.5 Touch Target Clearance: The center of each touch target has a distance of at least 10 mm from the center of any other touch target, except when the user has reduced the default scale of content. (Level AA) [MOBILE]

Then the techniques under 2.5.4 can go in here...

  *   [MOBILE] Multiple Elements: When multiple elements perform the same action or go to the same destination (e.g. link icon with link text), these should be contained within the same actionable element. This increases the touch target size for all users and benefits people with dexterity impairments. It also reduces the number of redundant focus targets, which benefits people using screen readers and keyboard/switch control.
  *   M002<http://w3c.github.io/Mobile-A11y-TF-Note/Techniques/M002> Touch Target: Ensuring that touch targets are at least 9mm.
Here's a discussion from a UX site that seems pretty solid ...
"Be sure to check for interference on each axis of a target. To avoid interference errors, make sure that touch targets are at least 8 millimeters apart on center—with 10-millimeter spacing being strongly preferable. On center is an engineering term that means when measured from the center of each touch target. In this way, you can be measure the distance between the centers of differently sized objects such as a link and a button, because neither the visual- nor the touch-target sizes matter in this measurement.
As a consequence, most touch targets will never be too closely adjacent to each other, and only small amounts of space are necessary between them. This space does not have to be visually apparent. A non-touch area need not necessarily be whitespace. For example, toolbars often comprise icons that have suitable spacing, but without any visual indication of the gap between them. And the height of a tab bar can be as narrow as you want visually, as long as no other targets are too close either above or below the tabs.
  http://www.uxmatters.com/mt/archives/2013/03/common-misconceptions-about-touch.php#sthash.sfRgVb65.dpuf


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