Looks like a classic 1:N relationship to me. "1" is the measurement session and "N" is all the measurements (i.e. data points) taken in that session. This is modeled by two tables and one foreign key between them, similar to this:
Tweak the fields to suit your needs, but this general design should be more than able to handle large amounts of data and varying numbers of measurements per session.
That being said, MS Access has historically had significant limitations on the size of the data that can be stored in a single database. If you hit these limits, consider using a "real" DBMS.