For example, we may choose a song to play to regulate our emotions or influence co-present others.

Many things we do with computers, such as listening to music or postingmessages, are about control.

Moreover, control theory offers a broad view of interaction; itis not limited to input.

In text entry, the theory provides us with concepts andmetrics that aid our understanding of typing performance.

For example, the information rate ofa text entry method can be quantified using the concept of throughput from information theory.

Even seemingly mundane activities such as enteringtext have rich structures that can be uncovered by these theories.