Manual studies have staff follow shoppers and draw their route, while surveys and focus groups ask customers afterwards. Both can capture things sensors miss, such as whether a shopper touched a product or put it back, or the make-up of a group. The trade-offs are cost, small samples, observer bias and timings that are hard to record precisely; surveys also rely on memory.
Shoppermotion measures passively and continuously. Tags on trolleys and baskets record every trip with timestamps, so dwell time, customer flow and conversion come from the whole population of tagged trips rather than a sample, and each trip is matched with its ticket.
When an observed study is the right tool, it does not have to be on paper. Digital Flow, also from Shoppermotion, lets coworkers draw each customer's path on a tablet, add events and demographics, and see results the moment they finish.