<http://schema.org/description>
"&lt;p&gt;Form or geometry gages are generally divided into two categories depending on what form parameters they are designed to measure.  While there is no formal designation to differentiate these two categories\u2014sometimes they are simply referred to as roundness or cylindricity gages\u2014their difference is primarily based on their ability to make self-referenced or datum-referenced measurements. &lt;/p&gt;"^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.mmsonline.com/columns/self--and-datum-referenced-form-measurements>