Random Section of GOST 21.404-85
2.9. Not all functional features of an instrument shall be reflected during the letter symbol legend development but only those used in the given diagram.
2.10. The letter A shall be used to denote the «alarm» functions irrespective of whether the alarm equipment is installed separately on a panel or alarm functions are fulfilled by the instrument built-in indicator lamps.
2.11. The letter S shall be used to denote an instrument contact element used only for switch-on, switch-off, switchover, and interlocking operations.
Once the contact element of the instrument is simultaneously used for switch-on, switch-off, and alarm operations, the S and A letters shall be used in the instrument legend.
2.12. The limiting values of the measured quantities used, for example, for switch-on, switch-off, interlocking, and alarm operations may be specified by adding the letters H and L, which shall be written on the right-hand side of the graphic symbol.
2.13. If it is necessary to specify the measured quantity on the right-hand side of the instrument graphic symbol, the quantity name or symbol may be used.
2.14. To denote quantities that are not mentioned in this Standard, backup letters may be used. The backup letter use shall be explained in the diagram.
2.15. The communication line input to the instrument shall be shown at any point of the graphic symbol (top, bottom, or side). Arrows shall be used to denote the signal direction in the communication lines where required.
2.16. The instrument symbol legend development philosophy is shown in drawing 3.