[jondubois]

>> Is it good enough to estimate the number of people inside by subtracting out counts from in counts?

> Yes. It's better than just an estimate

What if someone waved their hand in front of it (in a particular direction) in an attempt to subvert it? Couldn't someone trick it into over-reporting or under-reporting the number of people inside?

What if someone is standing idle in front of it (near the door frame) for a few minutes and in the meantime a large number of other people walk in? Will it miss them?

What if two or more people walked in at the same time with no gap between them?

Most importantly: How would the counter ever be able to correct itself from inaccuracies?