How do you calculate cryptocurrency average cost?

As a seasoned practitioner in the world of cryptocurrency and finance, I'm curious to understand the intricacies of calculating the average cost of cryptocurrency holdings. Could you elaborate on the methodology behind this process? Is it a simple arithmetic mean of all purchase prices, or does it involve more complex weighting systems that account for the quantity of each acquisition? Additionally, how do fluctuations in market value and the timing of transactions factor into this calculation? I'm particularly interested in understanding how to accurately track and assess the overall investment performance of my cryptocurrency portfolio.