A friend of mine has spent years metal detecting around this part of upstate New York, and occasionally he'll show me something that came out of a field we've probably driven past hundreds of times.

Some of the finds are ordinary enough: old copper coins, buttons, bits of hardware and tokens from businesses nobody remembers. Others reach surprisingly far back. One of my favorites is a Spanish silver two reales from the eighteenth century, roughly the diameter of a modern quarter.

It's difficult to hold an old coin without wondering what it once bought.

That's also where things become complicated, because translating money across centuries isn't as simple as converting one number into another. The coin contains a measurable amount of silver, but that doesn't tell us exactly what the silver meant to the person who carried it. Wages were different. Goods were produced differently. Some things that are cheap today were enormously expensive, while things we now spend considerable money on didn't exist at all.

Even so, the temptation to find a conversion is strong.

We want to know what the coin was really worth.

I've become increasingly suspicious of the question, or at least of the assumption hiding inside it. It suggests that somewhere underneath all the changing prices there must be a stable measure that will let us compare 1776 with 2026.

Dollars won't do it. A dollar today clearly doesn't buy what a dollar bought generations ago.

Silver won't quite do it either.

Neither will gold.

That doesn't make any of those measures useless. It means we're trying to measure a moving economy from inside the economy.

For long periods, gold and silver played a much more direct monetary role than they do in ordinary American commerce today. Spanish silver circulated widely in early America, and the monetary system that developed in the United States was strongly connected to existing silver coinage. Later monetary arrangements changed repeatedly, eventually leading to the Bretton Woods system, under which foreign governments and central banks could exchange dollars for gold at an official price.

That arrangement ended in 1971 when the United States stopped converting foreign official dollar holdings into gold.

It's tempting to draw a straight line there: before 1971 money represented something real, and afterward it became an abstraction.

History is messier than that.

Metallic monetary systems had inflation, deflation, financial crises, changing exchange ratios, shortages of coin and political arguments about what counted as money. Gold and silver themselves changed value relative to the things people needed.

What changed wasn't that money stopped having value.

The mechanism by which the monetary unit was defined changed.

That distinction matters because the dollar still works remarkably well for one of the things I ask money to do. If I buy groceries this afternoon, I don't need to calculate the price in ounces of silver, hours of labor or bushels of wheat. Dollars give everyone involved a common unit in which to quote prices and settle the transaction.

The trouble appears when I ask the same unit to carry information across long periods of time.

Suppose someone tells me that a house sold for $20,000 many decades ago.

I know the number.

I still don't know what it meant.

How much did the buyer earn? What interest rate did they pay? How large was the house? What did land cost in that particular place? How expensive were food, transportation and energy? How many years of work did the purchase represent?

The nominal price is real information, but it isn't enough information.

Economists have a term for one version of the confusion that follows: money illusion, our tendency to respond to nominal amounts without fully accounting for changes in purchasing power. A raise in the number printed on a paycheck, for example, doesn't necessarily mean someone can buy more with the paycheck.

Once you notice this, historical prices become much more interesting.

Instead of asking only what something cost, I start asking what it cost relative to something else.

How many hours of ordinary work bought it?

How much food?

How much land?

How much energy?

How much gold or silver?

Each comparison gives a different view, and none deserves to become the master measurement.

This is where I think my own understanding has changed over the years.

I once regarded precious metals as something closer to a fixed reference point. Dollars moved while the metal provided the ruler.

That isn't quite right.

As I write this in September 2026, gold is trading around $4,300 an ounce and silver around $64. Those numbers certainly tell us something about the relationship between dollars and precious metals, but they don't tell us why the relationship changed.

Gold can become more desirable.

Silver has substantial industrial demand.

Interest rates change the relative appeal of assets that don't produce income.

Mining costs and production change. Investment demand changes. Monetary conditions change. Expectations change.

The ruler moves too.

That doesn't make precious metals uninteresting as stores of value. It makes them participants in the same world we're trying to measure.

Once there is no privileged ruler, ratios become useful.

The gold-to-silver ratio tells us how those two assets are priced relative to one another. Home prices measured in wages tell us something different from home prices measured in dollars. Oil measured against wages gives another view. A stock index measured in gold can look quite different from the same index measured in dollars.

None reveals the hidden true price.

Together they give us more perspectives on what changed.

This is similar to trying to understand distance without realizing that the thing you're measuring from is also moving. One observation can be perfectly accurate within its frame and still give a misleading impression when treated as absolute.

Money makes this easy to forget because we write the unit everywhere.

$5.

$50.

$50,000.

The notation remains constant while what the numbers can command changes around it.

That old Spanish coin makes the problem tangible. I can weigh it. I can identify its metal content and learn something about where and when it was minted. With enough historical research, I can estimate some of the things a person might have exchanged it for.

What I can't do is produce one modern dollar figure that completely translates the economic experience of carrying it.

Maybe that's the more interesting lesson.

Money doesn't provide an external view of value. It's one of the relationships through which we observe value.

A dollar price tells us where something sits relative to dollars at a particular moment. A silver price gives another relationship. Wages give another. Time, scarcity, usefulness and circumstance continue moving underneath all of them.

The mistake isn't using the dollar as a ruler.

It's forgetting that the ruler moves too.