:Q: What's the difference between "double sentence spacing" and "striking the space bar twice between sentences"? 
 :A: "Double sentence spacing" can also be achieved by inserting a single word space between sentences that is twice the width of a normal word space. This can done by professional printing methods that allow variable spacing. However, depending on justification, this "double space" may not be exactly twice the width of a standard word space on every line. "Striking the space bar twice between sentences" is done when the average person creates text with a keyboard or uses a monospaced font. It will be exactly twice the width of a standard letter space.