In the following charts, note the difference in the price of crude oil when calculated in terms of Dollars vs. GoldGrams. In the Dollar chart the price of crude oil fluctuates AND gets increasingly more expensive, as shown by the rising red line. In the GoldGram chart the price of crude oil fluctuates but does not get more costly. In this case the red line remains steady. While the purchasing power of the Dollar shrinks, GoldGrams preserve their purchasing power.
Gold is fundamentally different from all other commodities in one very important respect.
Most commodities are produced for consumption. Gold is the exception because it is produced for accumulation. Conversely, very little gold is consumed, destroyed or lost. Cumulatively, this gold comprises the aboveground stock. Because these factors of supply and demand are nearly identical over the long-term, gold's purchasing power is maintained over time.