The big event was Reagan busting the air traffic control union. Union really busting took off afterwards since it was demonstrated the government would roll them for private sector interests. Unions that existed just became gutted of power and influence as a result and people stopped joining.

It says percent change, it’s not an absolut value.

Suppose that at a given moment a certain number of people are engaged in the manufacture of pins. They make as many pins as the world needs, working (say) eight hours a day. Someone makes an invention by which the same number of men can make twice as many pins as before. But the world does not need twice as many pins: pins are already so cheap that hardly any more will be bought at a lower price. In a sensible world everybody concerned in the manufacture of pins would take to working four hours instead of eight, and everything else would go on as before. But in the actual world this would be thought demoralizing. The men still work eight hours, there are too many pins, some employers go bankrupt, and half the men previously concerned in making pins are thrown out of work. There is, in the end, just as much leisure as on the other plan, but half the men are totally idle while half are still overworked. In this way it is insured that the unavoidable leisure shall cause misery all round instead of being a universal source of happiness. Can anything more insane be imagined?

–Bertrand Russell, In Praise of Idleness

In a factory setting, it’s the amount of product produced. In an office job, it’s a partially made-up metric based on whatever is important to the business.

“Percent change” according to the axis label. “Hourly compensation” is also in units of “percent change” which also kind of reeks.