Other examples of TmL that we have found ubiquitous, alongside appreciating models and their outputs, are reading graphs and being able to communicate the meanings of graphs in context. An example of this comes up in the selling of current account mortgages, which we have investigated. A standard “persuasive graphic” that is used with prospective customers shows the outstanding balance of the mortgage over time, and the effects on the graph of “offsetting” the mortgage debt against savings – that is, paying interest only on the difference between the outstanding mortgage and the savings held in the account – see the Figure below which shows the standard repayment of £100,000 borrowed over 20 years (grey line), compared with offsetting £20,000 of savings for the life of the mortgage (black line). By saving on interest, capital can be repaid more quickly, saving in the case shown several years on the mortgage term.
Outstanding balance £
100000 90000 80000 70000 60000 50000 40000 30000 20000
Figure: Outstanding balance graphs for a current account mortgage
Software-generated graphs like this are a key tool used in selling current account mortgages. The main point to be made to the customer is that discounted interest rates are not the only thing that matters about a mortgage, contrary to the way that most mortgages are sold. We found that sales agents had only the vaguest idea of how the graphs are calculated by the software, but as with the example discussed above, should it matter that the user of the tool does not know what the creator of the tool has done? We think it matters because key parameters for the mortgage are not visible in the graph, such as the interest rate and the monthly payment. Moreover, there would be a benefit in knowing something about how the parameters interrelate to determine the repayment characteristics. Managers say that sales employees need a better appreciation of how the different aspects of the current account mortgage fit together. Communicating attractive features of the mortgage involves a series of reasoning steps by which employees are able to link a customer concern or characteristic to a feature or benefit of the product. We are not advocating algebra refresher courses for sales staff. Rather, there is a need for employees to explore the relationships that are embedded in the model of the mortgage that is encoded in the software, and to reason about these