I'm not sure whether it's the Physicist in me or my love of Lost (The Constant) but I've been think about a 'constant' in the learner experience. 

Throughout their education and employment learners experience different Virtual Learning Enviroments. These are all variables. e.g. WebCT in schools, Blackboard in HE, and an organisational intranet within employment.

What any equation or learner needs is a constant. This is a Personalised Learning Environment.

The importance of this constant may be greater in Distance Learners, as maturer DL student may be in employment whilst studying at university, therefore have to use two systems simultaneously.