| direction of the action path in a functional diagram Note 1 to entry: In a functional block the direction of action goes from the input of the block to its output (see Figures 1 and 2). Note 2 to entry: The direction of action needs not be the same as the direction of mass or energy flow. Note 3 to entry: This entry was numbered 351-23-05 in IEC 60050-351:2006. 
Figure 1 – Functional diagram indicating typical elements of an elementary open-loop control system 
Figure 2 – Functional diagram indicating typical elements of an elementary closed-loop control system
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