If you have an NVIDIA Reflex enabled GPU you will find an option to enable the “Flash Indicator.” When enabling this option a small white square will be displayed when your primary fire button is first pressed. For users who have Reflex Latency Analyzer equipped monitors, you can use the flash indicator in conjunction with Geforce Experience to get real-time measurements of your total system latency. It is important that the flash indicator be displayed with our without Reflex enabled so that users can understand their total system latency in all scenarios.
NVIDIA also has a post to help provide some insight, here: https://nvidia.custhelp.com/app/answers/detail/a_id/5175
