# 4 Points

[4 Points] command generates a line segment after specifying a line(base line) that the line to generate lies on.

## Step 1

For the prompt "Specify the start point of the base line", specify the start point of the base line. An arbitrary point can be input.

## Step 2

For the prompt "Specify the terminate start point of the base line", specify the terminate point of the base line. An arbitrary point can be input.

## Step 3

For the prompt "Start point of the line", specify the start point of the line to generate. Mouse cursor point will be projected onto the base line.

## Step 4

For the prompt "Terminate point of the line", specify the terminate point of the line to generate. Mouse cursor point will be also projected onto the base line.

Pressing `B` key, the line segment length will be doubled by setting the previous input point be the middle point of the line.