XGeology Double Right Angle Prism
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<b>[Product Information]</b><br>
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<li>The Double Right-Angle Prism 90 : http://www.pobonline.com/articles/89550-back-to-basics</li>
<li>Fig. 26 A double prismatic square : http://www.fao.org/docrep/R7021E/r7021e05.htm#4.3.2 the double prismatic square</li>
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