How is this site?
https://katana1.com/making-windows-perfmon-uptime-metric-cim-compliant/
I'm already collecting the performance counter. By itself, fairly uninteresting in a single line chart. For example, if a machine is rebooted once per day, the line would have a sawtooth look. I'd like use that counter, calculate the flat part (as downtime) and apply a formula to provide the uptime in % over a period of time like 30 days, last 90 days, last year, etc.