*”Why are my results different between tool X and tool Y?”* is one of the most common questions asked in performance and one that has no easy answer. In an ideal world, speed metrics and results would be easily comparable and reliable, no matter where we look. Often, that’s not the case.

Obtaining the same results from different tools is close to impossible because of how networking, browsers work and speed testing works. The technical context might help understand the issue, but it doesn’t solve it.

Performance monitoring is a data modelling problem. If the methodology differs, so do the results. **While we want uniformity, what we must accept is divergence. **