<s>
The	O
ball-and-disk	B-Device
integrator	I-Device
is	O
a	O
key	O
component	O
of	O
many	O
advanced	O
mechanical	B-Device
computers	I-Device
.	O
</s>
<s>
Typical	O
uses	O
were	O
the	O
measurement	O
of	O
area	O
or	O
volume	O
of	O
material	O
in	O
industrial	O
settings	O
,	O
range-keeping	O
systems	O
on	O
ships	O
,	O
and	O
tachometric	B-Device
bombsights	I-Device
.	O
</s>
<s>
The	O
addition	O
of	O
the	O
torque	O
amplifier	O
by	O
Vannevar	O
Bush	O
led	O
to	O
the	O
differential	B-Device
analysers	I-Device
of	O
the	O
1930s	O
and	O
1940s	O
.	O
</s>
<s>
The	O
basic	O
concept	O
of	O
the	O
ball-and-disk	B-Device
integrator	I-Device
was	O
first	O
described	O
by	O
James	O
Thomson	O
,	O
brother	O
of	O
William	O
Thomson	O
,	O
1st	O
Baron	O
Kelvin	O
.	O
</s>
<s>
William	O
used	O
the	O
concept	O
to	O
build	O
the	O
Harmonic	B-Device
Analyser	I-Device
in	O
1886	O
.	O
</s>
<s>
A	O
number	O
of	O
similar	O
systems	O
followed	O
,	O
notably	O
those	O
of	O
Leonardo	O
Torres	O
y	O
Quevedo	O
,	O
a	O
Spanish	O
physicist	O
who	O
built	O
several	O
machines	O
for	O
solving	O
real	O
and	O
complex	O
roots	O
of	O
polynomials	O
;	O
and	O
Michelson	O
and	O
Stratton	O
,	O
whose	O
Harmonic	B-Device
Analyser	I-Device
performed	O
Fourier	O
analysis	O
,	O
but	O
using	O
an	O
array	O
of	O
80	O
springs	O
rather	O
than	O
Kelvin	O
integrators	O
.	O
</s>
<s>
The	O
solution	O
was	O
the	O
Dreyer	O
table	O
,	O
which	O
used	O
a	O
large	O
ball-and-disk	B-Device
integrator	I-Device
as	O
a	O
way	O
to	O
compare	O
the	O
motion	O
of	O
the	O
target	O
relative	O
to	O
the	O
ship	O
,	O
and	O
thereby	O
calculate	O
its	O
range	O
and	O
speed	O
.	O
</s>
<s>
The	O
US	O
Navy	O
used	O
a	O
somewhat	O
simpler	O
device	O
known	O
as	O
the	O
Rangekeeper	B-Device
,	O
but	O
this	O
also	O
saw	O
continual	O
modification	O
over	O
time	O
and	O
eventually	O
turned	O
into	O
a	O
system	O
of	O
equal	O
or	O
greater	O
sophistication	O
to	O
the	O
UK	O
versions	O
.	O
</s>
<s>
A	O
similar	O
calculator	O
formed	O
the	O
basis	O
of	O
the	O
Torpedo	B-Device
Data	I-Device
Computer	I-Device
,	O
which	O
solved	O
the	O
more	O
demanding	O
problem	O
of	O
the	O
very	O
long	O
engagement	O
times	O
of	O
torpedo	O
fire	O
.	O
</s>
<s>
A	O
well-known	O
example	O
is	O
the	O
Norden	B-Device
bombsight	I-Device
which	O
used	O
a	O
slight	O
variation	O
on	O
the	O
basic	O
design	O
,	O
replacing	O
the	O
ball	O
with	O
another	O
disk	O
.	O
</s>
