science

Key date

Key date is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Key date rather than just read about it. In short: A key date is a term used in coin collecting and it refers to a date (or date and mint mark combination) of a given coin series or coin set that is harder to obtain than other dates in the series. A key date coin is usually one with a lower mintage total and it is more valuable than others in the series.

Key takeaways

Key date belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Key date to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Key date from memory before moving on to harder problems.

Reference excerpt

A key date is a term used in coin collecting and it refers to a date (or date and mint mark combination) of a given coin series or coin set that is harder to obtain than other dates in the series. A key date coin is usually one with a lower mintage total and it is more valuable than others in the series. Many coin collectors collect coins to fill out a complete set of a series. There are also semi-key dates in coin collecting. A semi-key date coin is typically one that is not as rare as the key date. The semi-key date often sells for a premium over common date coins, but less than the cost of a key date coin.

Background A key date is the term for a coin which is scarcer and harder to obtain in a series. Often coins with certain years or Mint marks are key date coins. Some factors that influence whether a coin is a key date include: demand, quantity of coins struck, the population of surviving examples and rarity of mint state examples. The cost of the key date coins in a series are usually the most expensive to obtain. The coins are also often referred to as the rarest in a series. Key dates are an important component of coin collecting because many collectors collect coins which fill a coin set: key date coins are the most important. They are valued by collectors because they are needed to complete coin sets. For the United States collectors of the Lincoln cent series, the 1909-S VDB Lincoln Cent is the rarest and most expensive of cents. The 1909-S VDB Lincoln cent is considered to be a key date due to its low mintage of only 484,000. The United States 1893-S Morgan dollar is known as the key date in the Morgan series. The 1893-S Morgan dollars were struck at the United States San Francisco Mint. Only 100,000 coins were struck making it the lowest mintage of any business strike Morgan Dollar.

Semi-key date The next level of difficult to obtain coins in series are often referred to as semi-key dates or simply semi-keys. The semi-key date coins are scarce and sell for a premium but they are not as scarce and rare as a key date. There are not rules which determine which coins are semi-key dates. Some coin collectors the coins in the series with lower mintage figures to be semi-key dates.

Counterfeits Numismatic Guaranty Company (NGC) produced a list of counterfeited coins: many of them are key date coins. One of the most common methods of counterfeiting involves adding a mintmark to the coin, in order to turn it into a key date coin.

References

Further reading Pasek, Matthew (2017). US Key date coin hand-e-book 1892-present. Independently Published. ISBN 978-1549547751.

External links Key Date Coin Guides More Key Date Coin Guides

Illustrations

Worked examples

Example 1 — a first encounter with Key date

Start with the simplest possible case. Write down what Key date claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Key date before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Key date ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Key date

In research: Key date appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Key date in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Key date is common in secondary-school and first-year university syllabi. It links to neighbouring topics Coin collecting, Coins, Numismatics, so understanding it makes those chapters shorter.
In everyday life: Look for Key date outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Key date in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Key date means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Key date out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Key date in simple terms?

Why does Key date matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Key date?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Key date.