Before the early 1970s, hand-held electronic calculators were not yet in widespread use. Because of their utility in saving work in laborious calculations by hand on paper, tables of base-10 logarithms were found in appendices of many books. Base-10 logarithms were called **common logarithms**. Such a table of "common logarithms" gave the logarithm of each number in the left-hand column, which ran from 1 to 10 by small increments, perhaps 0.01 or 0.001. There was no need to include numbers not between 1 and 10, since if one wanted the logarithm of, for example, 120, one would know that

Similarly for numbers less than 1 we have

Common logarithms are sometimes also called *'Briggsian logarithms'\* after Henry Briggs, a 17th-century British mathematician.

Because base-10 logarithms were called "common", and engineers often had occasion to use them, engineers often wrote "log(*x*)" when they meant log_{10}(*x*). Mathematicians, on the other hand, wrote "log(*x*)" when they mean log_{e}(*x*) (see natural logarithm). Today, both notations are found among mathematicians. Since hand-held electronic calculators are designed by engineers rather than mathematicians, it became customary that they follow engineers' notation. So ironically, that notation, according to which one writes "ln(*x*)" when the natural logarithm is intended, may have been further popularized by the very invention that made the use of "common logarithms" obsolete: electronic calculators.