Brand and business goals remain the best way to measure impact of a promotional tactic. However, this truism is not always applied with new technologies
Many pharmaceutical companies are now selling with digital tablets, where almost every click the sales representative makes can be measured, and time tabulated. These tablets generate sequential data streams, which are sometimes measured with basic KPIs like time spent, and the order of tablet slides used.
This is reminiscent of the early days of website analytics ten years ago, where the metrics often cited were page views and time on website. Back then, those were used as KPIs because they were reportable in the elementary "web log" systems.
However, whether it's websites or sales tablets, the objective of engagement within a channel is to achieve a business goal. Therefore on websites, we now measure funnels to goal pages like CRM registrations, and consumption of segmented content areas.
The same should hold for sales force tablets. Think about your brand goals,and what particular sections of the tablet presentations are most aligned toward achieving those goals. Measure consumption of those sections as a valuable indicator of success.