Changing Display from extended to Duplicate

If you are using an instructor machine in a lab and run PowerPoint in presenter view it may keep the displays extended. To change to duplicate : 

For Windows based machines:

 Right click on an open area of the desktop and Display Settings. 

1. Under multiple displays, select "duplicate these displays", then click OK.

For Mac based machines:

1. Go to the menu Apple menu in the upper left hand corner and select system preferences.
2. Select Displays.
3. Go to Arrangement and select "mirror displays" to start mirroring the display.