Anyone using excel to track network (network devices only - switches, routers, T1's etc) downtime using percentages? I guess I just need to create a formula based on if a router was down for 5 minutes in a year, how much downtime in percentage that would be.

We have a few network monitoring tools such as IPMonitor. Zenos etc. However, the boss only wants initial information from excel. Being that I'm not an excel guru, anyone that can point out an example, that would be great.