References:

GDP data from: https://www.bea.gov/data/gdp/gross-domestic-product#gdp

Gold Data from: https://www.usagold.com/daily-gold-price-history/

S&P 500 Data from Finance Yahoo history: https://finance.yahoo.com/quote/%5EGSPC/history

National CPI Inflation data from: https://inflationdata.com/Inflation/Inflation_Rate/CurrentInflation.asp?reloaded=true

National Debt Data from: https://fiscaldata.treasury.gov/datasets/historical-debt-outstanding/historical-debt-outstanding

More Description:

The chart with Y axis logarithmic $ values was generated using MS Excel. There is an upper cluster of lines in USD $ as published (with Inflation), and a lower cluster of lines CPI Inflation SUBTRACTED. The upper cluster has two roughly parallel curvy plots using S&P 500 Monthly $ MAXIMUM values for the upper line and $ MINIMUM values for the lower line 1/1950 to latest on chart. The upper cluster has 2 straight lines a Best Fit Upper, and Best Fit Lower, which in effect represent one line with thickness or separation, value see chart legend.

FIT method: Fitting the Straight Lines to the S&P 500 plot was by accumulation of Log excess that is for increasing months adding positive differences for the upper plot above the upper Straight Line and negative differences for the lower plot below the lower Straight Line, giving an accumulating Area value starting 1/1950 to latest month on chart. The idea is that an Area above the straight line must be eventually negated by an Area below it to return to the long run average fixed compound interest climb. Where the accumulation has a Low Value (actual Value see Legend) of preceding Area accumulation this is a Best Fit month marked by a logic HIGH on the FIT graph. The final Best Fit was found by trying different Values of Percentage slope and different USD Starting points to achieve the highest number of FIT months, also observing the FIT graph and Sum of All months. Note: Separation of straight lines has minor effect; the non-accumulating Fit is insensitive to Values.

The lower cluster also has two roughly parallel S&P 500 curvy plots taken from the upper cluster S&P 500 plots but are LESS Inflation so look different and have less slope. The lower cluster has two additional parallel lines derived from the straight lines BFU and BFL but also without inflation so are now curvy. The lower cluster includes a straight line, added for guide and information, of a compound interest % per annum based in 1990, value see chart legend.

US GDP graphs With and Without inflation and US National Debt graph are valid only for percentage SLOPE to compare to the S&P 500, both base 1/1980. The chosen USD base is for clarity not on the S&P 500 value so that the graph isn’t drawn over it. It is interesting to note that the GDP graph % slope greatly underperforms the S&P 500 % slope and the Debt graph % slope somewhat matches the S&P 500 slope.

Gold is included as an interesting aside and $ per ounce Y scale is valid.