<s>
A	O
parametric	B-General_Concept
model	I-General_Concept
is	O
a	O
set	O
of	O
related	O
mathematical	O
equations	O
that	O
incorporates	O
variable	O
parameters	O
.	O
</s>
<s>
Software	O
project	O
managers	O
use	O
software	B-Application
parametric	I-Application
models	I-Application
and	O
parametric	O
estimation	O
tools	O
to	O
estimate	O
their	O
projects	O
 '	O
duration	O
,	O
staffing	O
and	O
cost	O
.	O
</s>
<s>
In	O
the	O
early	O
1980s	O
refinements	O
to	O
earlier	O
models	O
,	O
such	O
as	O
PRICE	O
S	O
and	O
SLIM	O
,	O
and	O
new	O
models	O
,	O
such	O
as	O
SPQR	O
,	O
Checkpoint	O
,	O
ESTIMACS	O
,	O
SEER-SEM	O
or	O
COCOMO	O
and	O
its	O
commercial	O
implementations	O
PCOC	O
,	O
Costimator	B-Application
,	O
GECOMO	O
,	O
COSTAR	O
and	O
Before	O
You	O
Leap	O
emerged	O
.	O
</s>
<s>
As	O
systems	O
became	O
more	O
complex	O
and	O
new	O
languages	O
emerged	O
,	O
different	O
software	B-Application
parametric	I-Application
models	I-Application
emerged	O
that	O
employed	O
new	O
cost	O
estimating	O
relationships	O
,	O
risk	O
analyzers	O
,	O
software	O
sizing	O
,	O
nonlinear	O
software	O
reuse	O
,	O
and	O
personnel	O
continuity	O
.	O
</s>
