Slide rules pushed science to normalize powers of ten
Scientific notation writes awkward magnitudes as m times ten to the n, usually with m's absolute value at least one and under ten. Slide-rule culture needed that standard form; computers still spit it for extremes. Engineering notation instead locks exponents to multiples of three.
Britain calls it standard form, and calculators label it SCI mode. The number in front is the significand, sometimes called the mantissa, a word that also names the fractional part of a common logarithm and so can confuse. Because 350 could be written 3.5, 35 or 350 times a power of ten, the normalized version fixes the leading figure between one and ten, which makes comparison quick: a bigger exponent always means a bigger number, and the gap between exponents estimates the orders of magnitude between them. Values below one take a negative exponent, so 0.5 becomes 5 times ten to the minus one.
Examples show the savings. An electron weighs 9.10938356 times ten to the minus 31 kilograms, the Earth 5.9724 times ten to the 24. Engineering notation, the ENG key, would give Earth's circumference as 40 times ten to the six metres, matching the SI prefix mega. The form also clears up significant figures: 1230400 is ambiguous, but 1.2304, 1.23040 or 1.230400 times ten to the six states exactly how many digits were measured.
Computers mostly write the exponent with a letter E, so Avogadro's number appears as 6.022E23. That convention came from Fortran's first release for the IBM 704 in 1956, and C, Python and JavaScript inherited it. ALGOL 60 used a subscript ten instead, a symbol so awkward for hardware that ALGOL W swapped in a single quote, some Soviet versions used the Cyrillic letter ю, and Unicode finally added the character in 2009.
Pocket calculators gained the feature in 1972, often showing the exponent as small raised digits after a blank. Style guides still discourage E notation in published work.
Source: Scientific notation
