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<p>Both those are describing the function of the instrument which is
the same in both cases and is not the point in question. Even so
the first definition includes the statement "<span
style="font-size:10.5pt;font-family:"Arial",sans-serif;color:#202122">In
formal engineering nomenclature, more precise terms are used to
distinguish the two.".<br>
</span></p>
<p>The PO's question was how do I connect a _tachometer_ , and the
answer to that is fundamentally different to a rev counter. A rev
counter displays the rate at which a cable drive is turning, a
tachometer measures the time between successive electrical
pulses. In the rev counter case it doesn't matter whether it is
on a 4, 6 or 8 (etc.) cylinder whereas for a tachometer the pulses
from an 8 cylinder engine are coming in at twice the rate of a
4-cylinder and there have to be _internal_ differences in the
tachometer to display that correctly. If the terms are used
interchangeably then when responding to a (formal engineering?)
question you would first have to establish which one is being
talked about!<br>
</p>
<p>PaulH.<br>
</p>
<div class="moz-cite-prefix">On 02/08/2023 14:29, dave northrup
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:f02a88b8d25648ad8effc0409adad964@ranteer.com">
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<p
style="mso-margin-top-alt:6.0pt;margin-right:0in;margin-bottom:6.0pt;margin-left:0in;background:white"><span
style="font-size:10.5pt;font-family:"Arial",sans-serif;color:#202122">From
Wikipedia<o:p></o:p></span></p>
<p
style="mso-margin-top-alt:6.0pt;margin-right:0in;margin-bottom:6.0pt;margin-left:0in;background:white"><span
style="font-size:10.5pt;font-family:"Arial",sans-serif;color:#202122">A <b>tachometer</b> (<b>revolution-counter</b>, <b>tach</b>, <b>rev-counter</b>, <b>RPM
gauge</b>) is an instrument measuring the rotation speed
of a <a href="https://en.wikipedia.org/wiki/Axle"
title="Axle" moz-do-not-send="true"><span
style="color:#3366CC;text-decoration:none">shaft</span></a> or
disk, as in a motor or other machine.</span><sup
id="cite_ref-1"><span
style="font-size:8.5pt;font-family:"Arial",sans-serif;color:#202122"><a
href="https://en.wikipedia.org/wiki/Tachometer#cite_note-1"
moz-do-not-send="true"><span
style="color:#3366CC;text-decoration:none">[1]</span></a></span></sup><span
style="font-size:10.5pt;font-family:"Arial",sans-serif;color:#202122"> The
device usually displays the <a
href="https://en.wikipedia.org/wiki/Revolutions_per_minute"
title="Revolutions per minute" moz-do-not-send="true"><span
style="color:#3366CC;text-decoration:none">revolutions
per minute</span></a> (RPM) on a calibrated analogue
dial, but digital displays are increasingly common.</span><span
style="font-size:10.5pt;font-family:"Arial",sans-serif;color:#202122"><o:p></o:p></span></p>
<p
style="mso-margin-top-alt:6.0pt;margin-right:0in;margin-bottom:6.0pt;margin-left:0in;background:white;font-variant-ligatures:
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2;text-align:start;widows: 2;-webkit-text-stroke-width:
0px;text-decoration-thickness: initial;text-decoration-style:
initial;text-decoration-color: initial;word-spacing:0px"> <span
style="font-size:10.5pt;font-family:"Arial",sans-serif;color:#202122">The
word comes from <a
href="https://en.wikipedia.org/wiki/Greek_language"
title="Greek language" moz-do-not-send="true"><span
style="color:#3366CC;text-decoration:none">Greek</span></a> τάχος (<i>táchos</i> "speed")
and μέτρον (<i>métron</i> "measure"). Essentially the words
tachometer and <a
href="https://en.wikipedia.org/wiki/Speedometer"
title="Speedometer" moz-do-not-send="true"><span
style="color:#3366CC;text-decoration:none">speedometer</span></a> have
identical meaning: a device that measures speed. It is by
arbitrary convention that in the automotive world one is
used for engine revolutions and the other for vehicle speed.
In formal engineering nomenclature, more precise terms are
used to distinguish the two.<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">From dictionary.com<o:p></o:p></p>
<p class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><b><span
style="font-size:36.0pt;font-family:"Arial",sans-serif">tachometer<o:p></o:p></span></b></p>
<p class="MsoNormal"><span
style="font-size:13.5pt;font-family:"Arial",sans-serif">[
ta-<b>kom</b>-i-ter, t<i>uh</i>- ]</span><span
style="font-family:"Arial",sans-serif">SHOW IPA<o:p></o:p></span></p>
<p class="MsoNormal"><!--[if gte vml 1]><v:shapetype id="_x0000_t75" coordsize="21600,21600" o:spt="75" o:preferrelative="t" path="m@4@5l@4@11@9@11@9@5xe" filled="f" stroked="f">
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<div class="MsoNormal"
style="margin-bottom:15.0pt;text-align:center" align="center">
<hr width="100%" size="2" align="center"> </div>
<p class="MsoNormal" style="margin-bottom:15.0pt"><i><span
style="font-size:13.5pt;font-family:"Arial",sans-serif;color:black">noun</span></i><span
style="font-size:13.5pt;font-family:"Arial",sans-serif;color:black"><o:p></o:p></span></p>
<ol style="margin-top:0in" type="1" start="1">
<li class="MsoNormal" style="color:black;mso-list:l0 level1
lfo1"><span
style="font-size:13.5pt;font-family:"Arial",sans-serif">any
of various instruments for measuring or indicating
velocity or speed, as of a machine, a river, or the blood.<o:p></o:p></span></li>
<li class="MsoNormal" style="color:black;mso-list:l0 level1
lfo1"><span
style="font-size:13.5pt;font-family:"Arial",sans-serif">an
instrument measuring revolutions per minute, as of an
engine.</span></li>
</ol>
</div>
<br>
</blockquote>
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