In 1900 a 20 dollar coin contained 0.9675 ounces of gold. An ounce of gold was legally defined as $20.67. No free floating gold price. A dollar coin contained 1.672 grams of gold.

1900 $1 is equal to 2025 $172

So a single dollar today will buy 1/172 of what it would in 1900. That is inflation. Not an inflation adjusted curve. Just the drastic devaluation of the dollar.

A single dollar today will buy 1/172 of what it would in 1900, as long as what you're buying is gold. If you are buying anything else, though, your number is not relevant. And that means that your number is useless, because it's only the number if you're buying gold, and gold is almost never what we actually want to buy.

The curve suggests that there would also be periods of inflation and deflation, for instance of a market basket of goods and services, under a gold standard.