I actually thought the FTC outlawed, or ruled against vacuum manufacturers using Horse Power ratings for vacuums.
From Wikipedia:
Horsepower is a unit measure of how much work is done. There are many different standards and types of horsepower.
Units called "horsepower" have differing definitions:
<ul>
<li>The
mechanical horsepower, also known as
imperial horsepower, of exactly 550
foot-pounds per second is approximately equivalent to 745.7 watts. (A 3 hp motor would draw 2,237.1 watts. More than is available in an American outlet.)</li>
<li>The
metric horsepower of 75
kgf-m per second is approximately equivalent to 735.5 watts or 98.6% of an
imperial mechanical horsepower.
<ul>
<li>The
Pferdestärke PS (German translation of horsepower) is a name for a group of similar power measurements used in Germany around the end of the 19th century, all of about one metric horsepower in size.<sup id="cite_ref-4" class="reference">
<span style="font-size: small;">[</span><span style="font-size: small;">4</span><span style="font-size: small;">]</span></sup><sup id="cite_ref-5" class="reference">
<span style="font-size: small;">[</span><span style="font-size: small;">5</span><span style="font-size: small;">]</span></sup><sup id="cite_ref-6" class="reference">
<span style="font-size: small;">[</span><span style="font-size: small;">6</span><span style="font-size: small;">]</span></sup></li>
</ul>
</li>
<li>The
boiler horsepower is used for rating steam
boilers and is equivalent to 34.5 pounds (about 15.6 kg) of water evaporated per hour at 212 degrees
Fahrenheit (100 degrees Celsius), or 9809.5 watts.</li>
<li>One horsepower for rating
electric motors is equal to 746 watts.</li>
<li>Continental European electric motors used to have dual ratings, using a conversion rate of 0.735 kW for 1 hp</li>
<li>British
Royal Automobile Club (RAC) horsepower is one of the
tax horsepower systems adopted around Europe which make an estimate based on several engine dimensions.</li>
</ul>
The link spells it pretty clearly
FTC: Truth in advertising ruled that vacuum motor either didn't reach or only reached peak horsepower for .0083 seconds on start up. Not sufficient for a horsepower claim.
This is why vacuums started listing amperage, which was also deceptive, but have so far been able to prove they reach Peak amps.
http://units called "horsepower" have differing definitions: