Lowry Research has some very good papers on tops and bottoms. You can D/L some white papers at the link below. PS Tops are much harder to spot than bottoms. https://www.lowryresearch.com/Research/WhitePapers
Indeed they do, and you need a strategy for exactly that. This is why I am averse to backtesting, etc.
From that chart, seems the 20th/21st century is a massive bubble. Took 100 years at a time to go up 10-fold between 1500 and 1900. Since then, it has been nearly 200-times in 100 years. Any reason for this?
I'll take a stab at it. The industrial revolution, causing a massive rise in productivity, followed by the invention of the computer, now the hand held computer, causing another large rise in productivity. The period of the 70s, sort of in between both, was a period of stagnation overall.
actually current time characterized by lower productivity and many attribute it to handheld computers
There's also the matter of companies being valued according to earnings rather than dividends, which gave rise to earnings multiples and price-to-earnings ratios. In the late 90s, many companies were valued according to projected earnings and earnings multiples and attracted tons of money even though they had no earnings at all. Then of course there's inflation and the effect that has on unadjusted prices. I'm sure an inflation-adjusted market price can be found somewhere on line.
You can do it in reverse, and it's a little bit easier to see. Go back to 1975, before personal computers, fax machines, modern diesel engines, and all the other stuff that's been invented since partly because of those things, and tell me how much the average company is worth. Now do it in 1920, before autos became adopted. Now do it in 1870, before electric motors, lightbulbs and telephones. How much was your average company worth then? Oh, that's right, they didn't exist.