RUM: Changes to how some metrics are calculated

15 March 2023 (UTC)

We have identified and fixed a long-standing bug in the way some RUM metrics are calculated. Previously, values of zero (0) would be ignored when calculating metrics. This did not affect most metrics however some metrics often do have a value of zero, including (but not limited to):

  • First Input Delay (FID) - users on fast devices who interact with a page may experience no input delay. The FID value that we record is rounded to the nearest millisecond, so any delay that is less than 0.5ms will be recorded as zero (0ms).
  • Network times such as DNS lookup and TCP connect - caching at various layers can result in network times being recorded as zero.

As a result of this bug being fixed, you may noticed a drop in some of your RUM metrics, including the ones mentioned above.