The pica is a unit of length in the field of typography and uses the symbol pc.
There are 12 points in 1 pica. 1 pica represents approximately 1/6 of an inch.
Picas are expressed using numbers and a lower case p on software such as Adobe InDesign - for example 8p6 which would represent 8 picas and 6 points (or 8.5 picas).
The Pica is very useful in measuring and calculating the space needed to print letters and words on paper - for example when laying out books or magazine articles; the font lengths are quanitified by the number of characters per pica (cpp).
The angstrom (or ångström) is a unit of length and is a non-SI but metric accepted unit with the symbol Å.
It is equal in length to one ten-billionth of a metre or 0.1 nanometres (0.1nm).
It is approximately the size of an atom and is mostly used to measure very small distances for example wavelengths of light.