# What is an surface-perpendicular wheel control called?

Please bear with me as I attempt to describe this control (since I don't know its name I wasn't able to google image search for it).

It's a physical control, used for adjusting a quantity up or down. Imagine a disk, maybe 1/4 inch in thickness, with notches around its circumference at regular intervals. Now take the disk and, holding it perpendicular to a control board (the same way a car wheel is perpendicular to the road), imagine sinking it into the board until only a little bit of the disk is still visible, sticking out if the top of the board like an iceberg out of water. You can now use your thumb to rotate the disc in place by pushing on the part sticking out. This rotation changes the value of whatever quantity you are controlling.

What is a such a control called?

Have you seen skeuomorphic versions of them used in mobile apps, and what are the usability issues around them?

In aviation this is called a "trim tab" or a "trim wheel":

In this context, it is used to adjust control surfaces (commonly the elevator), so that the "hands-off" pitch of the aircraft is maintained at the angle the pilot wants.

Another, probably more universally familiar context, are classic hand-held transistor radios:

On a hunch, I searched for transistor radio parts lists to see if I could find a manifest that listed this control by name. In my spare time I've been playing around with Arduino projects, and this type of control is called a potentiometer.

I believe the particular implementation we're talking about here is informally called a "disk type" potentiometer--it's basically just a low profile pot:

## So what should you call it?

I think it would be safe to call it a "trimmer", "disk potentiometer", or "disk pot". Of the three, "trimmer" would probably work for your context.

• A potentiometer is the electronic device ( a circular variable resister) not the type of control described though. Nov 26, 2014 at 11:06

Regarding the skeuomorphic versions of them used in mobile apps they seem to be referred to as

• Thanks, this is related, but not exactly what I meant. I've seen these, of course, since they're just the iphone version of a dropdown. But what I was imagining would be closer to just the middle section (with just the days, or just notches instead of days) and I'd also be interested in a version oriented horizontally rather than vertically. Oh and also, I'm imagining an always visible control, rather than one that pops up when you are selecting the value, as these do (at least in my experience) Nov 26, 2014 at 15:28
• There aren't really engineering names which are that specific to types of controls - your best bet would be to flick through many pages of the RS electronics catalogue uk.rs-online.com/web/c/switches/rotary-switches-accessories Nov 26, 2014 at 19:52