Average pace is a simple division: distance covered over time spent covering it. The part runners rarely question is which time. Total elapsed time, the stopwatch running from the moment you start to the moment you stop, includes every red light, every dog-walker you wait to pass, every gate you stop to open. Moving time only counts the seconds you were actually moving. Use the wrong one and the same run produces two different numbers, and only one of them describes how you actually ran.

The division that hides the problem

Pace is distance divided by time, and a stop adds seconds to the denominator without adding meters to the numerator. That's the whole mechanism. It doesn't matter whether the stop was 10 seconds at a crossing or two minutes waiting for traffic, every second gets treated identically by a calculation that only sees elapsed time: more time, same distance, worse pace. The run itself didn't get slower. The clock kept counting while your legs did not.

Why a few stops add up faster than it feels

A single light rarely feels like it matters. The trouble is that elapsed time is cumulative across the whole run, so three lights at 20 seconds each and one longer wait at a busy crossing can add up to a couple of minutes of standing still folded into a 25 or 30 minute run. Spread across that shorter a distance, a couple of minutes of dead time moves the average pace by a real, visible amount, often enough to make an otherwise solid run look mediocre in the log. The effect is proportionally worse on shorter runs. A stop that barely dents an hour-long long run can swing a fast 5K's average pace by a noticeable margin, since the same fixed number of stopped seconds is a much bigger share of a shorter total.

Moving time asks a different question

Moving time answers "how fast was I while I was actually running," which is a different question from "how long did this whole outing take, door to door." Both numbers are legitimate, they're just not interchangeable. Total elapsed time is honest about how long you were out. Moving time is honest about how you ran when you were running. Reporting only the first one as your "average pace" quietly answers the second question with the wrong number, which is exactly why the same effort can look faster or slower run to run depending on how many times traffic happened to stop you, rather than on anything you actually did differently.

What tells the two apart

The only way to separate elapsed time from moving time is to know when you were actually stopped, which is what auto-pause is for. A tracker that detects a real stop, as opposed to a brief GPS wobble or a red light you jogged through, can hold onto that stopped duration separately from the stopwatch and subtract it back out later. Without that detection, there's no way to tell a deliberate two-minute wait at a crossing apart from two minutes of just slow, tired running, and the calculation has to fall back to total elapsed time by default, stops and all.

How Zirv handles it

The average pace attached to a saved run in Zirv is calculated from moving time, not raw elapsed time: the total duration has the time auto-pause counted as stopped subtracted out before distance gets divided by what's left. A run with a couple of light stops folded in still records the pace you were actually holding while running, not a number quietly dragged down by however much traffic you happened to hit that day. That's also why the numbers are worth reading against your own history rather than a single run in isolation, the same way running cadence is more useful as a trend than a single data point: a pace trend built on moving time compares like with like, run to run, regardless of how many crossings each one happened to include.

The takeaway

Average pace is only as honest as the time it's divided by. Total elapsed time counts every stoplight as if you were running through it, which punishes runs with more stops for a reason that has nothing to do with fitness. Moving time asks the more useful question, how fast were you actually running while you were running, and answering it requires knowing when you were genuinely stopped rather than just guessing from the stopwatch. A pace number that holds up across a training block is one measured the same way every time, stoplights and all.