To analyse the function of a product, service or process can be done with the Function tress techniques. FAST Diagram Method and the Subtract and Operate Procedures are the two techniques in functional trees method. Function Analysis and System Technique is one of the technique to develop a graphical representation to show the logical relationship between the function of a project, product process with the help of questions “How” and “why”.

## Function Analysis and System Technique

The Function Analysis and System Technique (FAST) is used to define, analyze and understand product functions, how the functions relate to one another and which functions require attention to increase product value.

It is used to display functions in a logical sequence, priorities them, and test their dependency.

### FAST Procedure

- The first step is to brainstorm all the functions the product will serve in the eyes of the customer.
- The function should be defined as broad and generic as possible, such as produce torque, generate light, shape material etc.
- The
**basic function**is the overall product function. For example, the basic function of a car seat belt is to restrain a person in a car seat. - The
**Secondary functions**:- these are essential to the performance of the basic function and they are direct cause to the basic function. - Secondary functions can be categorized into 3 types
- Required
- Aesthetic
- Unwanted by product

- With FAST, the function tree is established by asking “How is the function is achieved?” to each function, starting with the basic function. The answer may be one or several.
- Overall function is placed at the top left of the diagram. The sub-functions resulting from how questioning are listed to the right of the overall functions.
- This string of sub-functions that are critical to achieving the product function is called Critical Path.
**Other Functions**must be listed at the top of the Fast diagram.- All Time Functions are functions that are pervasive to the product. Listed on the right of the diagram.
- One Time Functions are functions are listed at the centre of the diagram.

## How to draw FAST Diagram for a Product?

Let us take an example look at how a FAST diagram looks like for a product. Then we can understand the steps very easily.

- Construct two vertical dashed lines. One to the extreme left and one to the right. These lines define the scope of the product development objective.
- Place the basic function to the left side of the left-hand scope line. Pose the question, “How is the function is achieved?” A higher-order function will answer this question. Place this function to the left of the basic function and connect with a line, beginning the critical path.
- Generate functions to the right of the basic function. These functions should always follow a how and why answering scheme and represent the secondary functions. Connect these functions with lines to define the furtherance of the critical path.
- The critical path will end with an “assumed function,” outside the right scope line. This function is external to the product. Such as “supply electricity” in the case of an Iron box.
- Generate the remaining secondary functions by placing them under the functions that relate to the basic or critical path secondary functions. These functions either occur at the same time or are caused by the functions on the critical path.
- State the objective of the development effort above the basic function. In addition, add one-time or all-time functions to the top of the diagram.

This is all about the Function Analysis and System Technique in the product design course.

## Conclusion

We have discussed the Function Analysis and System Technique of the sample product Iron box, if you still have any thoughts n this topic, let us know in the comment section below.

Manoj Mathur says

I shall be obliged to get reply from you.

You have explained ” Place the basic function to the right of the left-hand scope line” Sir as I understand BASIC FUNCTION as per me is IRONING THE CLOTHES & Not the PROVIDE ELECTRICITY SUPPLY.

Can you please clarify?

Sundar Dannana says

Hello Manoj,

Yes, you are absolutely right. The basic function is left side and it should be Ironing Cloths.

I have made a small correction in the above article. Let me know if you still have any doubts.

Also, we are very happy that you wanted to help us.