Referring to the Sample
Copying is confounded by counting and matching one tile at a time.
Images are used to make comparisons between the sample and their copy, seen as looking back and forth.
Measure the time interval between comparisons in seconds: in your head, and 2 or 3 intervals if they are inconsistent.
Count the number of times the person refers to the sample during sustained attention.
If the frequency of comparisons diminishes, estimate the time when they started making fewer glances to the sample.