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    10 <!DOCTYPE concept

    11   PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

    12 <concept id="GUID-5486EFD3-4660-4C19-A007-286DE48F6EEF" xml:lang="en"><title>Scale

    13 and positioning of controls</title><prolog><metadata><keywords/></metadata></prolog><conbody>

    14 <section id="GUID-EF8CA4BE-130F-4117-9722-3F652DD1D244"> <p>Interface elements

    15 a user has to select and manipulate should not be smaller than the smallest

    16 average finger pad, that is, no smaller than 1 cm (0.4") in diameter or a

    17 1 cm × 1 cm square.</p> <p>In the Symbian OS, UI style defines

    18 the target minimum sizes for a UI element considered as finger usable:</p><ul>

    19 <li><p>7 x 7 mm with 1 mm gaps for index finger usage</p></li>

    20 <li><p>8 x 8 mm with 2 mm gaps for thumb usage</p></li>

    21 <li><p>List type of components should have minimum of 5 mm line spacing</p></li>

    22 </ul><p>The width of a finger limits the density of items on screen. If the

    23 items are too close, the user will not be able to choose a single one.</p><p>As

    24 the user is more likely to touch higher on the button by mistake than either

    25 side, button and icon sizes can be increased vertically.</p><p>Essential information

    26 or features, such as a label, instructions, or sub-controls should never be

    27 placed below an interface element that can be touched, as it may be hidden

    28 by the user's own body.</p><fig id="GUID-FF8225A9-0D9F-4E8F-8B19-32FAECEFE47C">

    29 <image href="GUID-FD85921E-AC9F-481F-8A58-0D03D56661C0_d0e47154_href.png" scale="60" placement="inline"/>

    30 </fig><ul>

    31 <li><p>With interfaces with traditional input devices, it makes sense to place

    32 targets like menu items on the edges of screens: the user cannot overshoot

    33 the target, as the cursor stops at the edge of the screen. </p></li>

    34 <li><p>When using a touch screen, a user seldom drags his finger across the

    35 screen as he would with a cursor. Instead, they most likely lift their finger

    36 and place it on a new target. Users may have difficulties in reaching the

    37 objects located on the edges of the screen, especially if the physical device

    38 has protruding edges around the touch screen panel. Additionally, with some

    39 devices, the screen edges may be less sensitive to register the touch input.</p></li>

    40 </ul> </section>

    41 </conbody></concept>