deltaTime is the time in seconds it took to complete the last frame.

• 0.01666 if you are getting 60fps (1 divided by 60)
• 0.03333 if you are getting 30fps

Multiplying by deltaTime will make sure things happen in units per second, instead of units per frame.

If you do not multiply by deltaTime, you will get different values on different devices. On faster machines, objects will move faster and be further ahead of objects on slower machines.

• When to Use?
• Examples
  • Moving an object along the X axis
• Notes

When to Use?

Usually when you have code that needs to do something over time.

• Moving any object over time.
• Incrementing a number over time.

Examples

Moving an object along the X axis

public Transform _cube;

void Update()
{
	// Move the cube 1 unit per frame along the X axis (to the right)
	_cube.Translate(1f, 0f, 0f);
}

If you have a frame-rate of 60, after 1 second, the cube will be at position (60, 0, 0).

If you have a frame-rate of 30, after 1 second, the cube will be at position (30, 0, 0).

Not good!

public Transform _cube;

void Update()
{
    // Move the cube 1 unit per second along the X axis (to the right)
	_cube.Translate(1f * Time.deltaTime, 0f, 0f);
}

After 1 second, the cube will be at position (1, 0, 0), regardless of frame-rate. Everyone gets the same result.

Good!

Notes

• http://docs.unity3d.com/ScriptReference/Time-deltaTime.html
• http://forum.unity3d.com/threads/the-truth-about-fixedupdate.231637/#post-2442966
• http://fabiensanglard.net/timer_and_framerate/index.php