Braun here from Human Precision. The screen can only present a visual change on a display cycle, and the rest of the device adds more latency. Here is the practical explanation and the limit that matters when using a browser test.
What refresh rate changes
A display running at a higher refresh rate has shorter intervals between possible screen updates. That can reduce one part of the delay between the browser preparing a visual signal and the user seeing it. It does not remove input, operating-system or browser latency.
Refresh rate is not the whole device
Two screens with the same advertised refresh rate can still differ in processing and pixel response. Touchscreen input, mouse polling and system load also influence when an event reaches the test. Research on bring-your-own-device cognitive testing identifies both display-output and input latency as meaningful sources of measurement variation.
Browser timing remains useful
Human Precision uses performance.now(), a browser timing API designed for high-resolution elapsed-time measurements. That makes repeated local measurements practical, but it does not calibrate the physical display or input hardware.
How to compare fairly
Keep the same display, browser and input method. Avoid comparing a mobile touchscreen score directly with a desktop mouse score. Human Precision stores device-labelled personal history so the most useful competition is against your own prior setup.
What not to buy for one score
A faster monitor may change browser-test results, but a single online score is not a reason to make an expensive purchase. Use the test as a repeatable challenge. Read mouse versus touchscreen differences and try the six-skill daily test.
Human Precision provides recreational browser measurements. Device latency, practice, attention and environment affect results. Do not use a score for medical, education, employment, driving or safety decisions.