operation done on pre-paged versions of ITS, WAITS, and TOPS-10 was
sardonically referred to as `The Big BLT'). The jargon usage has
outlasted the {PDP-10} BLock Transfer instruction from which
{BLT} derives; nowadays, the assembler mnemonic {BLT} almost
always means `Branch if Less Than zero'.

:Blue Book: /n./ 1. Informal name for one of the three standard
references on the page-layout and graphics-control language
{{PostScript}} ("PostScript Language Tutorial and Cookbook",
Adobe Systems, Addison-Wesley 1985, QA76.73.P67P68, ISBN
0-201-10179-3); the other three official guides are known as the
{Green Book}, the {Red Book}, and the {White Book} (sense
2). 2. Informal name for one of the three standard references on
Smalltalk: "Smalltalk-80: The Language and its
Implementation", David Robson, Addison-Wesley 1983, QA76.8.S635G64,
ISBN 0-201-11371-63 (this book also has green and red siblings).
3. Any of the 1988 standards issued by the CCITT's ninth plenary
assembly. These include, among other things, the X.400 email spec
and the Group 1 through 4 fax standards. See also {{book
titles}}.

:blue box: /n./ 1. obs. Once upon a time, before
all-digital switches made it possible for the phone companies to
move them out of band, one could actually hear the switching tones
used to route long-distance calls. Early {phreaker}s built
devices called `blue boxes' that could reproduce these tones,
which could be used to commandeer portions of the phone network.
(This was not as hard as it may sound; one early phreak acquired
the sobriquet `Captain Crunch' after he proved that he could
generate switching tones with a plastic whistle pulled out of a box