I've just started using Ping Plotter. Thanks for this cool utility!

When ping times are logged and sent via an email alert, what is the difference when the time is listed as * or N/A?

An asterisk (*) means that there was no response from that host/router. This is known as a timeout, or a lost packet.

A N/A means that there wasn't *supposed* to be a response from that host/router. This happens if another host or router responds for that hop (ie: oscillating route), or if you've stopped tracing for a time, and then resume.

In an alert, the most likely cause of this (N/A) is because of a route change - where a host/router wasn't in the route for one or more samples - and another host responded in it's place. For that situation, a N/A is shown.