Nybble

I own several abaci and two books on how to use them, but they all have four counters below the bar and one counter above it. […] The bottom four counters of each abacus can be used to represent a "nybble," and the upper counter on each can be used for parity.

At every negative-going transition it reads a 4-bit ADPCM nybble (there are 2 nybbles per byte) and stores it in a memory-resident table.

Data is being received by a system in serial sequences of four bit nybbles. (A nybble is usually defined as a four bit grouping.) […] Our mission, should we decide to accept it, is to test each nybble and determine whether or not the four bits constitute a valid BCD (8421) number.

Similarly, it's easy to convert a binary number such as %1100011010110010 into its hexadecimal equivalent. All we have to do is to split the binary value into 4-bit nybbles and to map each nybble onto its corresponding hexadecimal digit.