Even when you are in the middle of a task, you can measure distances using Measure Distance. For example, consider the following workflow.
On the Draw toolbar, select Line/Arc Continuous and draw a line.
Click Tools > Measure Distance and measure a distance.
You do not need to exit Line/Arc Continuous before measuring a distance.
Right-click to exit Measure Distance. Line/Arc Continuous is still active—you can pick up where you left off and continue using Line/Arc Continuous.