Q. What is the difference between Gun time and Mat time?

When the official time is Gun time (rarely a gun, more often a count down to a hooter/"Go"), entrant times are calculated from when the first "gun" for an event distance was recorded to when the entrant's tag was recorded on the finish line. Placings are consequently calculated on Gun time.

Not everyone can (or does) start (cross the start line) on the gun. Knowing this some events choose to have results calculated on Mat time. Mat time is the elapsed time from the last time a tag is recorded crossing a designated start line, until the first time the same tag is recorded crossing a designated finish line. 

So which is more accurate: mat or gun time. The truth, when producing results for events, is a somewhat grey area.

For events where merit prizes are based on the order one reaches the finish, the times for those placings are derived from the gun times, that is the elapsed time between when the "Gun" started the event and when an entrant reaches the finish line. The "truth" of these placings can be verified by the cameras at the finish, and to a lesser extent by the more variable memories of those involved. So one truth is that everyone finishes in a ranking determined by the order they cross the finish line. When merit prizes are awarded by gun times, then gun times are given priority. Are these times misleading?

Well another truth is everyone crosses the start line at a different time so has a unique mat to mat time, and this time for everyone but a few in the starting row will be significantly faster than the gun time. If mat times are given priority, are these times misleading? Not in terms of reflecting the entrant's actual net time, but the results produced from them in terms of rankings/finish order do not reflect the finish order seen by spectators or recorded on camera.

When we display times we also display places, and these placings must reflect the type of time, i.e. if we show gun times as the official time we must show results calculated by gun time, and when we show mat times as the official time, rankings must be calculated on mat time. If not there would be serious grounds to challenge the maths!

The elephant in the room is that everyone wants (and generally deserves) to have their best time shown. This is why your certificate may for some events display only your mat time.

The problem for us if we were to display only mat times when gun times are the basis for awarding prizes occurs arises when a vociferous minority of entrants in any event choose to pursue a claim to a prize/reward on grounds that their mat time would gain them a place when the event rules state awards are determined by gun time.