Joseph M. Kadenge
When the Mars Climate Orbiter (MCO) was approaching Mars in September 1999, its main engine was supposed to slow down the spacecraft to place it in the orbit 150 km above the surface. It failed and MCO entered the atmosphere and was destroyed by stress and friction. The failure was completely due to a mix up unit of measurement between imperial units and SI units. The total cost was USD 327.6 million (1999).
The company which was subcontracted to manufacture MCO uses imperial units while NASA uses SI units. In its comment in relation to the incidence, NASA’s statement said “People sometimes make errors”. The amount of USD 327.6 million lost is equivalent to Tanzanian Shillings 524 billion at the current exchange rate of 1,600 TZS per 1 USD.
An accurate and consistent system of measurement is the foundation of a healthy economy. In Tanzania a motorist buys gasoline in liters while a jeweler sells gold in ounces. Land is sold in acres, fruits and vegetables are sold in piles (mafungu), while electric cables are sold in meters.
Without a consistent, honest system of measurement, world trade would be thrown into chaos. From ancient times to the present there has been a need for measuring things accurately. When the ancient Egyptians built monuments like the pyramids, they measured the stones they cut using body dimensions every worker could relate to. Small distances were measured in “digits” (the width of a finger) and longer distances in “cubits” (the length from the tip of the elbow to the tip of the middle finger; 1 cubit = 28 digits). The Romans were famous road builders and measured distances in “paces” (1 pace = two steps). Archaeologists have uncovered ancient Roman roads and found “mile”-stones marking each 1000 paces (mil is Latin for 1000).
The Danes were a seafaring people and particularly interested in knowing the depth of water in shipping channels. They measured soundings in “fathoms” (the distance from the tip of the middle finger on one hand to the tip of the middle finger on the other) so navigators could easily visualize how much clearance their boats would have. In England distances were defined with reference to body features of the king. A “yard” was the circumference of his waist; an “inch” was the width of his thumb, and a “foot” the length of his foot. English farmers, however, estimated lengths in something they could more easily relate to: “furlongs”, the length of an average plowed furrow.
Although the traditional system is still widely used in Tanzania, scientists prefer to use the metric system. Unlike the English (traditional) system, i.e. foot, yard, inch and the like; the metric system did not evolve from a variety of ancient measurement systems, but was a logical, simplified system developed in Europe during the seventeenth and eighteenth centuries. The metric system is now the mandatory system of measurement in every country of the world except the United States, Liberia and Burma (Myanmar).
In 1960, an international conference was called to standardize the metric system. The International System of Units (SI) was established in which all units of measurement are based upon seven base units: meter (distance), kilogram (mass), second (time), ampere (electrical current), Kelvin (temperature), mole (quantity), and candela (luminous intensity). The metric system simplifies measurement by using a single base unit for each quantity and by establishing decimal relationships among the various units of that same quantity. For example, the meter is the base unit of length and other necessary units are simple multiples or sub-multiples:
1 meter = 0.001 kilometer = 1,000 millimeters =1,000,000 micrometers = 1,000,000,000 nanometers
There are only 26 letters in the English alphabet, yet with these 26 letters it is possible to construct all of the words in the English language. Similarly, there are 7 “letters” in the “language of measurement” from which all units of measurement are derived. These 7 “letters” are distance, mass, time, electric charge; temperature, amount, and luminous intensity. These are known as the fundamental units because they cannot be expressed in a simpler fashion. All other units are derived from these seven units.
Distance is a fundamental unit, because it can be expressed in no simpler terms. However, volume is a derived unit because it is expressed as the cube of distance. For example, when measuring the volume of a box you multiply its length by its width by its height. The resulting volume is expressed as a cube of distance (d3) such as cubic feet or cubic centimeters. Density is also a derived unit because it is expressed as the ratio of mass/volume, where volume itself is a derived unit expressed as a function of distance cubed. Thus, we can express density (a derived unit) in terms of fundamental units as mass divided by distance cubed (m/d3).
Usefulness of units of measurement
We use units every day, often without even realizing it, in measurements, business, home, monetary system just to mention a few. Think about in business: Everything that is bought or sold has dimensions. A land investor needs to know if a tract is measured in acres, hectares, square feet, or square miles. A commodities broker needs to know if rice is priced by the gunia (sack), fungu (pile), lumbesa (extended gunia) or kilogram. A building contractor needs to know whether a developer has given him an order for concrete order in cubic meters or cubic feet. It would be nearly impossible to run a successful business without knowledge of the units of the trade.
Recipes always specify measurements in units. You need to know whether your recipe is measured in tablespoons, teaspoons, cups, quarts, gallons, milliliters or liters! When cooking dinner, it is essential that you know whether directions were written for a stove calibrated in Celsius or Fahrenheit.
In monetary matters, each country has its own monetary system. Although countries may use the same unit, it may have a different meaning. A Tanzanian Shilling does not value the same as Kenyan Shilling, neither is a Canadian dollar worth an American dollar. The full name of the unit should be specified whenever doing calculations. In other words, it is necessary to specify Tanzanian shilling, not just a shilling.
The importance of units of measurements in our daily lives cannot be overemphasized. But it is imperative to know the meaning of the units by which something is measured. On business reports you may hear the price of a particular commodity quoted. Although they may say that it costs $1000 per ton, the question remains, are they quoting the price per long ton (1.016 metric tons), per short ton (0.97 metric tons), or per metric ton?
To understand the world around us, it is necessary to know how items are measured, and what the units they are measured in represent. Putting things in a nutshell, measurements are the basis for decisions. To make an informed decision, you need information and the information is very often some kind of measures. Making decisions implies knowledge of measurements. In this regard, Lord Kelvin once said “If you cannot measure it, you cannot improve it.”
*Mr. Kadenge is a Metrologist in the TBS Metrology Laboratory.