Hi,

If column A:A contains dates and column B:B contains uptime then

=AVERAGE(B:B)/16

should give you the uptime percentage, if you format the cell as %. It
will be dynamic, as it will change as more values are entered in B:B.
This will give you the total uptime since you started monitoring, so
naturally with time it should converge to your overall average.

Write back if you want something more specific, e.g. the average of the
last X days.

HTH
Kostis Vezerides