Block and Arrows:

While blocks are used to identify several categories of mathematical operations, operations of further and subtraction are represented through a circle, known as a summing point.  As display in Figure, a summing point might have one or various inputs.  Every input has its own suitable plus or minus sign. The summing point has only one output and is equal to the algebraic sum of the inputs.

Block and Arrows

Figure: Summing Points

A takeoff point is used to permit a signal to be used through more than one block or summing point.

Figure: Takeoff Point