what is the basic about Fisher FirstVue and how is it used in calculating flow

<...how can one understand the reading of P&ID and equally use it in extracting instrument index....>

The P&ID is supposed to be a lead document, showing the principal items of equipment, the piping interconnections and the instrumentation selected for a particulat plant. With the P&ID should be a symbology sheet, which may be either project-specific or a corporate Standard, which should give full details of how to interpret the symbology.

The symbols on the P&ID must be followed to produce an instrument index. Some of these will be physical instruments, like a field-mounted temperature transmitter for example, or they may be "virtual" instruments, like a high temperature alarm that is derived from the temperature signal and some sort of comparison arrangement within a control system.

In order to derive correctly the instrument schedule, the P&ID should be used to produce a Control Philosophy, usually written by the Process Engineer in collaboration with the Controls Engineer, which states how the plant is intended to work. It is an incoming document to the Controls Engineer, who in response will produce the Functional Design Specification, in collaboration with the Process Engineer, that states how the control system will achieve what is stated in the Control Philosophy.

<...how can one go about cable scheduling in instrumentation?...>

This is the task of the Controls Engineer, who will determine from the layout of the plant and its controls locations the equipment and the cabling required to achieve a correct installation. This individual will have on-board the implications of any hazardous area zoning requirements that will influence what goes where. Local cabling standards and the physical layout of the plant are essential features of getting the cable schedule correct, though, being cables, it is a relatively minor task to add or delete cables as the design proceeds.