符号的选择遵循以下原则:a）植物应广泛使用；b） 符号应易于绘制，且易于区分；c） 应表示原理，而不是任何特定类型机器的外观。d）如果单个符号表示一组项目，且单独的符号在国家标准化，则ISO符号应易于与任何一个国家符号区分。

The symbols have been selected in accordance with the following principles: a) the plants should be widely used; b) the symbols should be easy to draw and readily be distinguishable one from another; c) the principle and not the appearance of any particular type of machine should be represented, d) where a single symbol represents a group of items for which separate symbols are s-tandardized nationally, the ISO symbol should be readily distinguishable from any one of the national symbols.