数字选择 meaning in English

digital selective calling

Customers have the choice of specifying valve size as part of the valve figure ( " b " ) using the numbers below , or indicating valve size separately
用户使用下列数字选择特定的阀门通径作为阀门型号（ b ）的一部分，或另行指明阀门通径。
Global maritime distress and safety system - part 3 : digital selective calling equipment - operational and performance requirements , methods of testing and required testing results
海上呼救和安全装置.第3部分:数字选择呼叫装置.操作和功能要求.试验方法和规定试验结果