Illustration showing when <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \theta =1\mathrm {rad} }"><semantics><mrow class="MJX-TeXAtom-ORD"><mstyle displaystyle="true" scriptlevel="0"><mi>θ<!-- θ --></mi><mo>=</mo><mn>1</mn><mrow class="MJX-TeXAtom-ORD"><mi mathvariant="normal">r</mi><mi mathvariant="normal">a</mi><mi mathvariant="normal">d</mi></mrow></mstyle></mrow><annotation encoding="application/x-tex">{\displaystyle \theta =1\mathrm {rad} }</annotation></semantics></math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/3ddba54bd2f387188599a5f9dfbdf830505afae5" class="mwe-math-fallback-image-inline" aria-hidden="true" style="vertical-align: -0.338ex; width:8.718ex; height:2.176ex;" alt="{\displaystyle \theta =1\mathrm {rad} }"></span>.
<a href="//commons.wikimedia.org/wiki/User:Gustavb" title="User:Gustavb">Gustavb</a>
<span class="int-own-work" lang="en">Own work</span>