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The term numerical control actually refers to two distinct functions that are interrelated. The term numerical refers specifically to the instructional information applied to the machine. This generally represents digital information punched into a paper tape（纸带） or card that is read by the input part of the system. Two-state conditions such as holes or no holes in apaper tape are used to instruct the machine.The digital console（控制板） is primarily srsponsible for this operation.
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The Windows operating environment gives the user an almost infinite range of expressing text. As multimedia programmer, you can choose what font to display text in , how big (or small) it should be, and what colour it should be displayed in. By displaying text in more than one format, the message a multimedia application is trying to portray can be made more understandable.
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How does the dc motor react to the application of a shaft load（轴类负载）? What is the mechanism（机制） by which the dc motor adapts itself to supply to the load the power it demands? The answers to these questions can be obtained by reasoning(推理) in terms of the performance equations（方程）. Initially our remarks are confined to(局限于) the shunt motor, but a similar line of reasoning applies for the others. For our purposes the two pertinent（相关的） equations are those for torque and current. Thus
