Every figure, name, date and setting the finished video puts on screen, chased to a source.
The oscillator reports where the close sits inside the high to low range of a lookback window, expressed as a percentage of that range. It is not a reading of how high or low price is in absolute terms.
%K = (Current Close - Lowest Low) / (Highest High - Lowest Low) * 100
%D = 3-day SMA of %K
Zero is the bottom of the window and one hundred is the top.
%K is the faster line and %D is the slower one, and %D is a moving average of %K rather than a separate measurement. On the standard setting %D is a three period simple moving average of %K.
TradingView’s Stochastic ships with %K Length 14, %K Smoothing 3 and %D Smoothing 3, and with the overbought line at 80 and the oversold line at 20. StockCharts documents the same trio as the default parameters of the Full Stochastic Oscillator, and the same two thresholds.
The 14 is the lookback: a 14 period %K uses the most recent close, the highest high of the last 14 periods and the lowest low of the last 14 periods.
This is the video’s central claim and it is stated outright by the reference documentation.
Overbought readings aren’t necessarily bearish. Securities can become overbought and remain overbought during a strong uptrend. Closing levels that are consistently near the top of the range indicate sustained buying pressure.
The same source records George Lane’s own description of what the indicator follows:
It follows the speed or the momentum of price. As a rule, the momentum changes direction before price.
Lane, 1921 to 2004, worked at Investment Educators in Illinois and was part of a group of Chicago futures traders who developed the oscillator. He is credited with popularising it, which is the claim the video makes, rather than with sole authorship: the roles of Lane and C. Ralph Dystant in its origin are a documented and long running debate, and the earliest written articulation of the %K and %D oscillator dates to 1957.
Bullish divergence is price making a lower low while the oscillator makes a higher low; bearish divergence is price making a higher high while the oscillator makes a lower high. Both describe momentum, and neither is by itself a statement that direction has changed, which is the distinction the video turns on.
Where the video sets three configurations against each other to show the trade off between a faster and a smoother reading, the two either side of the default are chosen to bracket it rather than reported as anybody’s published default. Only 14, 3, 3 is presented as a platform default, and that one is sourced above.