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===Michael Murtaugh – Slide Rule (in leather carrying case)===
Once an invaluable device for every engineer (you may note how the case is designed to be affixed to its operator's belt), the slide rule is maybe best described as an analog calculator.  Unlike a modern digital calculator, the slide rule requires the (human) calculator to mentally maintain the correct order of magnitude (or scale of a calculation) meaning that calculated quantities are overtly contingent on the knowledge of the operator rather than presented as seemingly absolute and precise external fact.

[[Image:IOK2015_4.2_Ochshorn_InterLace.jpg|thumb|link=Ideographies_of_Knowledge/Session_4#Robert_M_Ochshorn_.E2.80.93_InterLace|258px|[[Ideographies_of_Knowledge/Session_4#Robert_M_Ochshorn_.E2.80.93_InterLace|'''Video''']] ]]