If "lag" is a metric describing latency from source to display, then based on displaylag.com (and whatever other goofballs), my CRT has 16.67ms of lag, or 8.3ms if you take the middle bar.
Right, 8.3ms is correct though. CRTs aren't technically 'zero lag' because they still have to write from top to bottom, and that takes time, however quickly. We measure from the middle because that's generally where we're looking. Display manufacturers like to measure from the top because it makes the numbers better. Neither is really right or wrong, but middle feels reasonable to me for 'real world' use.
It's somewhat meaningless, we're not capably of detecting 8 milliseconds like that, but it's there in terms of the physics of it.