<s>
An	O
optical	O
comparator	O
(	O
often	O
called	O
just	O
a	O
comparator	O
in	O
context	O
)	O
or	O
profile	B-General_Concept
projector	I-General_Concept
is	O
a	O
device	O
that	O
applies	O
the	O
principles	O
of	O
optics	B-Algorithm
to	O
the	O
inspection	O
of	O
manufactured	O
parts	O
.	O
</s>
<s>
Hartness	O
 '	O
long-continuing	O
work	O
as	O
the	O
Chairman	O
of	O
the	O
U.S.	O
'	O
s	O
National	O
Screw-Thread	O
Commission	O
led	O
him	O
to	O
apply	O
his	O
familiarity	O
with	O
optics	B-Algorithm
(	O
from	O
his	O
avocations	O
of	O
astronomy	O
and	O
telescope-building	O
)	O
to	O
the	O
problem	O
of	O
screw	O
thread	O
inspection	O
.	O
</s>
<s>
The	O
idea	O
of	O
mixing	O
optics	B-Algorithm
and	O
measurement	O
,	O
and	O
the	O
use	O
of	O
the	O
term	O
comparator	O
for	O
metrological	O
equipment	O
,	O
had	O
existed	O
in	O
other	O
forms	O
prior	O
to	O
Hartness	O
's	O
work	O
;	O
but	O
they	O
had	O
remained	O
in	O
realms	O
of	O
pure	O
science	O
(	O
such	O
as	O
telescopy	O
and	O
microscopy	O
)	O
and	O
highly	O
specialized	O
applied	O
science	O
(	O
such	O
as	O
comparing	O
master	O
measuring	O
standards	O
)	O
.	O
</s>
<s>
The	O
profile	B-General_Concept
projector	I-General_Concept
is	O
widely	O
used	O
for	O
complex-shape	O
stampings	B-Application
,	O
gears	O
,	O
cams	O
,	O
threads	O
and	O
comparing	O
the	O
measured	O
contour	O
model	O
.	O
</s>
<s>
The	O
profile	B-General_Concept
projector	I-General_Concept
is	O
hence	O
widely	O
used	O
in	O
precision	O
machinery	O
manufacturing	O
,	O
including	O
aviation	O
,	O
aerospace	O
industry	O
,	O
watches	O
and	O
clocks	O
,	O
electronics	O
,	O
instrumentation	O
industry	O
,	O
research	O
institutes	O
and	O
detection	O
metering	O
stations	O
at	O
all	O
levels	O
,	O
etc	O
.	O
</s>
<s>
It	O
can	O
be	O
simpler	O
as	O
well	O
as	O
reduce	O
errors	O
by	O
measuring	O
on	O
the	O
magnified	O
projection	O
screen	O
of	O
a	O
profile	B-General_Concept
projector	I-General_Concept
.	O
</s>
<s>
A	O
profile	B-General_Concept
projector	I-General_Concept
may	O
also	O
have	O
episcopic	O
illumination	O
(	O
which	O
is	O
light	O
shining	O
from	O
above	O
)	O
.	O
</s>
<s>
For	O
the	O
simplest	O
type	O
of	O
profile	B-General_Concept
projector	I-General_Concept
,	O
the	O
part	O
's	O
inverted	O
image	O
,	O
also	O
known	O
as	O
its	O
mirror	O
image	O
,	O
will	O
be	O
displayed	O
on	O
the	O
screen	O
.	O
</s>
