Consistency is a principle that can add a lot to the ease of systems. Below are three examples from my life that have elements of consistent design.
Example 1: Television Remote
This is a great example of an external, functional consistency. The remote itself is a universal remote made by Logitech, but the true consistency in this product comes not from itself but other remote controls from pretty much every company. Symbols such as play and pause, the addition of arrows and an enter button and the numbers 0-9 are all common elements in these products. This leads to people knowing the how to use the remote from past experiences. All the different systems share these features to make the learning process much easier.
Example 2: Printer
This Brother printer demonstrates aesthetic consistency in an internal way. Expectations of the printer’s systems are created from images used throughout. The most obvious example are the primary functions of print, fax, scan, copy and photo capture each represented by the same images on the outside of the printer and within the system. This consistent use of internal symbols helps users to relate everything within the printer to one of those aforementioned functions. Again this makes everything within the system easier and thus better designed.
Example 3: Ladder
Ladders can represent all types of consistency. On the external and functional sides one can expect a good ladder to be stable and easy enough to climb. Even when items such as ladders come in a variety of designs (as seen in the picture) consistencies such as these often carry over. While internally expectations can come from both aesthetics and functions. For example, it can be assumed each rung is the same length apart for proper safety while climbing up. All these examples on something as simple as a ladder proves the effectiveness of consistent design.