This is my theory which could be completely wrong.
I think floors are based on changes in barometric pressure. I live on the 4th floor of a 14 story condo building. With the pandemic lockdown and my gym being closed, I walk the floors pretty much every day. When I reach the top floor, I should show 10 floors climbed. Most times, my VA3 shows 9 floors climbed which is close enough for my purposes. I showed 10 only one time and 8 floors about 25% of the time.
However back in February, after walking for an hour on the beach in Fort Lauderdale, my watch recorded 82 floors climbed. I liken that to the difference in barometric pressure near the ocean vs. my hotel room about a mile inland.
Consider calibrating the altimeter before an activity, especially when the weather (and hence the barometric pressure) changes. Also make sure the pressure sensor orifice is clean, dry, and free of debris. Some models, with the orifice close to the skin, tend to clog with sweat during an activity which then easily leads to odd pressure readings. If it is your case, make sure to keep the skin dry under the orifice - drying it out with a sleeve, or just fingers of the other hand, up and then.
Some tip how to keep the floors numbers accurate are available in the following thread:
