Inspired by a post from Michael Tuminello in response to a question I had on the IxDA list, I propose this rule of thumb: “The same, or different, but not similar!“

The concept that Michael discussed (and I have said in the past in different terms), is that when designing, controls/patterns for similar functions across products (or even within the same product) should either be exactly the same (consistent) or vastly different. But they should never be “similar”. Being similar will result in many more usability issues than being entirely different where the user does not have certain expectations for behavior.

Selecting reporting time frames should be consistent across a suite of reporting products. If one product has vastly different constraints on time selection, requiring a different time selection mechanism, it should be obvious to the user that they are working with a completely different control with different behavior.