why do we use engineering notation instead of scientific notation
Scientific notation Engineering notation (often named "ENG" display mode on scientific calculators) differs from normalized scientific notation in that the exponent n is restricted to multiples of 3. Consequently, the absolute value of m is in the range 1 ≤ |m| < 1000, rather than 1 ≤ |m| < 10. Though similar in concept, engineering notation is rarely called scientific notation. Engineering notation allows the numbers to explicitly match their corresponding SI prefixes, which facilitates reading and oral communication. For example, 6992125000000000000♠12.5×10−9 m can be read as "twelve-point-five nanometers" and written as 6992125000000000000♠12.5 nm, while its scientific notation equivalent 6992125000000000000♠1.25×10−8 m would likely be read out as "one-point-two-five times ten-to-the-negative-eight meters".
History of the metric system In 1837 the metric system was re-adopted by France, and also during the first half of the 19th century was adopted by the scientific community. In the middle of the century, James Clerk Maxwell put forward the concept of a coherent system where a small number of units of measure were defined as base units, and all other units of measure, called derived units, were defined in terms of the base units. Maxwell proposed three base units: length, mass and time. This concept worked well with mechanics, but attempts to describe electromagnetic forces in terms of these units encountered difficulties. By the end of the 19th century, four principal variants of the metric system were in use for the measurement of electromagnetic phenomena: three based on the centimetre–gram–second system of units (CGS system), and one on the metre-kilogram-second system of units (MKS system). This impasse was resolved by Giovanni Giorgi, who in 1901 proved that a coherent system that incorporated electromagnetic units had to have an electromagnetic unit as a fourth base unit.