The figure on its own is close to useless, because it rises just as happily when people leave as when output goes up. This splits every move into the part that came from revenue and the part that came from headcount, and tells you which story you are actually in.
Most boards do not track this at all, and the ones that do usually quote a single number with no idea which half of the fraction moved.
Nothing you type leaves your browser unless you choose to save it. No figures are compared to anybody else's and none are published.
Whole years, halves or quarters, as long as they are the same length as each other. Headcount is full time equivalent at the end of the period.
A price rise moves this figure. So does a hiring freeze, a good year in one division, a disposal, or a contract that happened to land in March. If output per person went up, this tells you that it did. It cannot tell you why, and anybody presenting it as proof of an AI programme will be picked apart by the first person in the room who knows the numbers.
What it is genuinely good for is the argument before the work starts. If the plan is to get more done with the team you have, this is the figure that would move if the plan worked, and agreeing that up front is worth more than any amount of measuring afterwards.
Saving gives you an address you can bookmark, or send to whoever else needs to see it. No account, and nobody who opens it sees your email.
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If you want this figure to move without anybody leaving, the work is finding which tasks can be done in half the time and which must not be touched. That is a different tool, and then a room.