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It is not hard to obtain
{/it qualitative} statements about the amount
of coding saved and the amount of time lost when
subroutines are used. Suppose that a piece of coding
requires $k$ locations and that it appears in $m$
places in the pro-gram.
Rewriting this as a subroutine, we need
an extra instruction
{\tt STJ}
and an exit line for the subroutine,
plus a single
{\tt JMP}
instruction in each of the $m$ places
where the subroutine is called. This gives a total
of $m+k+2$ locations, rather than $mk$,
so the amount saved is
$$(m-1)(k-1)-3.\eqno(2)$$
If $k$ is 1 or $m$ is 1 we cannot possibly
save any space by using subroutines; this,
of course, is obvious. If $k$ is 2, $m$ must be 
greater than 4 in order to gain, etc.

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