Final answer:
Merlin is recording the frequency of picking his nose each day.
Step-by-step explanation:
Merlin is recording the frequency of picking his nose each day. Frequency refers to the number of times an event occurs within a given time period. In this case, Merlin is counting the number of times he picks his nose, which is a measure of frequency. The other dimensions mentioned: topography, intensity, and duration, are not applicable to the act of picking one's nose.