To ensure accurate recall of the experimental data, at minimum one should:

videotape the experiment
take digital pictures of the experiment
make sure at least two people are observing the experiment
record the data in writing

record the data in writing

Explanation:

Recording the data in writing is a standard practice of recording the outcomes of the experimental data. As the outcomes of the scientific procedure can be qualitative or quantitative data. The qualitative data will include the quality features like color, shape, features and characteristics. The quantitative data of the experiment will include the measurable data or the data which can be counted.

As repeated procedures and trials are required for the experimental process it will be easy, convenient and reliable to record the readings in writing. Instead of videography or taking a picture record which are not feasible for every trial of the experiment. Also due to lack of human resource two people may not be available as witness of the experimental procedure.