MORSE CODE
26 letters and 10 digits · dot, dash
Free
PHONETIC ALPHABET
the ICAO standard · for radio and telephone
$2.50
IMPERIAL UNITS
convert in your head · without a calculator
Free
PAPER SIZES
the A series · from A0 to A6
$1.50
SI PREFIXES
from quetta to quecto · twenty multipliers
$1.50