Decimalisation (or decimalization, with both spellings widely accepted) refers to the fundamental process of converting a system—be it currency or weights and measures—to units that are consistently related by powers of 10. This transition aims to simplify calculations, enhance clarity, and streamline transactions by establishing a logical, base-10 relationship between different denominations or units.

The inherent simplicity of the decimal system, which aligns with our base-10 number system, makes arithmetic significantly easier compared to traditional, often complex, non-decimal systems. Instead of juggling multiple, arbitrary conversion factors, users merely need to multiply or divide by powers of 10, typically by shifting a decimal point.

Currency Decimalisation: A Global Standard

The vast majority of countries worldwide have embraced decimal currencies, moving away from intricate non-decimal structures. In a decimal currency system, there is one primary unit (e.g., dollar, euro, pound) and sub-units that are fractions of this main unit, specifically by powers of 10. The most common relationship is 100 sub-units to one main unit (e.g., 1 dollar = 100 cents, 1 euro = 100 cents). Less frequently, a ratio of 1000 sub-units may be observed, such as 1 Kuwaiti Dinar equaling 1000 fils.

This conversion often involved not just the numerical relationship but sometimes also a change in the currency's name or its exchange rate against other currencies. Prior to decimalisation, many currencies featured complex relationships. For instance, the pre-1971 British currency system was famously non-decimal: 1 pound sterling (£) was equal to 20 shillings, and 1 shilling was equal to 12 pence, meaning 1 pound consisted of 240 pence. Converting between these denominations required non-trivial calculations, which decimalisation fundamentally eliminated.

The Pioneering Role of Russia

Russia holds the distinction of being the first country to formally adopt a decimal currency. Under the reformist reign of Tsar Peter the Great in 1704, the Russian ruble was officially set at 100 kopeks. This forward-thinking decision was part of Peter the Great's broader efforts to modernize Russia and align it with Western European standards of the time, predating many other nations by centuries.

The Few Remaining Non-Decimal Currencies (Theoretically)

As of today, only two countries technically maintain non-decimal currencies: Mauritania and Madagascar. In Mauritania, 1 ouguiya is divided into 5 khoums. Similarly, in Madagascar, 1 ariary is equal to 5 iraimbilanja. However, this non-decimal status is largely theoretical in practice.

The value of the main currency units in both nations is so low that their respective sub-units (khoums and iraimbilanja) are practically worthless. Consequently, coins for these sub-units are no longer minted or used in daily transactions. This means that, de facto, commerce operates using whole units of ouguiya and ariary, rendering them effectively decimalised in everyday use.

Metrication: Decimalisation of Weights and Measures

When decimalisation is applied to units of weights and measures, it is more commonly known as metrication. This involves replacing traditional systems that often relied on varied, arbitrary, or historically evolved conversion factors with the coherent, base-10 structure of the metric system.

For example, traditional units might be related by successive doubling or halving (like pints and quarts) or by factors like 12 (inches to feet), 16 (ounces to pounds), or 3 (feet to yards). Such systems often required memorization of numerous unrelated conversion values, making calculations cumbersome.

The metric system, by contrast, introduced a scientific and rational framework where units of physical measurement—such as length, mass, and volume—are related by powers of 10. This means that a kilometre is precisely 1000 metres, a kilogram is 1000 grams, and a litre is 1000 millilitres. This standardized approach significantly simplifies scientific work, international trade, and engineering projects.

Global Adoption and Notable Exceptions

The metric system has achieved near-universal adoption across the globe, becoming the standard for most scientific, industrial, and commercial applications. Its logical structure and ease of use have made it indispensable for international communication and cooperation. However, there are two prominent exceptions:

• The United States: Primarily uses the U.S. Customary System, which is derived from the British Imperial System and retains non-decimal relationships (e.g., 1 mile = 1,760 yards, 1 pound = 16 ounces).
• The United Kingdom: While officially metric for many purposes, the UK still maintains a mixed system, with some traditional imperial units remaining in common use, particularly for road distances (miles) and liquid measures (pints for beverages).

Universality of Decimal Electrical Units

In the realm of electrical units, decimalisation is universally applied. Units such as volts, amperes, watts, and ohms inherently follow the metric system's base-10 prefixes (e.g., kilovolt, milliampere, megawatt). This consistency ensures global compatibility and simplifies calculations in electrical engineering and electronics.

The Undecimalised Frontier: Time

Despite the widespread adoption of decimal systems for currency and measurements, common units of time—seconds, minutes, hours, days, weeks, months, years—have largely remained undecimalised. Our current system is rooted in ancient astronomical observations and cultural traditions, dividing hours into 60 minutes, minutes into 60 seconds, and days into 24 hours.

An notable attempt to decimalise time occurred during the French Revolution. Driven by a desire for complete rationalization and scientific consistency, the revolutionaries introduced a decimal calendar and decimal time. This system divided the day into 10 decimal hours, each with 100 decimal minutes, and each decimal minute into 100 decimal seconds. The week was extended to 10 days, and the year was organized into 12 months of 30 days, with five or six supplementary days. However, this radical change proved highly unpopular and impractical. Deeply ingrained cultural habits, the astronomical basis of the existing calendar, and the sheer inconvenience of relearning time measurement led to its rapid abandonment, reaffirming the enduring nature of our sexagesimal (base-60) and duodecimal (base-12) time divisions.

Frequently Asked Questions About Decimalisation

What is the primary benefit of decimalisation?

The primary benefit is simplified calculation and conversion. By relating units through powers of 10, arithmetic becomes straightforward, reducing errors and saving time in financial transactions, scientific work, and daily life.

Why are Mauritania and Madagascar considered "theoretically" non-decimal?

While their official currency systems define sub-units with a non-decimal relationship (1 main unit = 5 sub-units), the value of these sub-units is so low that they are not used in practice. All transactions effectively occur in whole units, making them de facto decimal.

What is the difference between decimalisation and metrication?

Decimalisation is the general concept of converting to a base-10 system. Metrication is the specific application of decimalisation to weights and measures, implementing the metric system.

Why did decimal time fail during the French Revolution?

Decimal time failed largely due to strong cultural resistance, the impracticality of redefining centuries-old habits, and the system's disconnection from astronomical realities which govern cycles like days and years.