Trials and Tribulations of Boring Interfaces

I’m often struck by how even the most straightforward and standard interfaces are cumbersome to get right. I know, I know, I’m the first to admit I don’t get stuff right all that often, especially not at the first go, but hear me out. Imagine the following object:

It’s something which is used often in hardware control panels, but less often in software UI. Most notably, when it is used in software it’s mostly when the software is specifically designed to mimic hardware, such as audio mixing boards. This is actually a shame, because a dial provides a number of benefits over linear sliders. For one, it is potentially infinite. You can keep turning it and turning it all the while changing the value. This is not possible with a linear slider. Also, the farther away the mouse is from the dial, the more accurate the control becomes, as the angle between two adjacent pixels is much smaller from the dial’s point of view:

The angle α is larger than β because the green pixels are closer to the dial than the blue pixels. So as users we can adjust how much effect a radial mouse displacement has simply by moving the cursor towards or away from the dial. Although one could implement a similar effect in linear sliders (the further away the mouse from the slider, the less the effect of a mouse translation), it would not be anywhere near as intuitive and controllable as the native behaviour of the dial.

But I came here to complain about boring interfaces, and a tuning dial is not boring, even though you might feel it is annoying. The boring bit comes in when we need to make the dial behaviour customizable. Is the value limited to some domain? If yes, what is this domain? What is the range of a single full turn? And so on and so forth. Simply putting all these values on a window would certainly allow users to adjust the dial and I’d bet a lot of programs simply take this approach and leave it at that.

But there’s a problem, some user settings depend on other user settings, which means not all possible values result in valid states, allow me to elaborate. The minimum limit should not be equal to or higher than the maximum limit and —conversely— the maximum limit should not be equal to or less than the minimum limit. How do we enforce this rule? Take some time to think about how you would encode this constraint.