Two nozzle booms use "flood jet" tips spaced 40 inches apart.  They spray a very wide angle pattern with a course droplet.  They work well with common broadleaf weed killers and lawn insect control chemicals. 

The five nozzle and larger booms use "flat fan" tips spaced 20 inches apart.  These tips will still work with the previous chemicals and will provide a finer more even spray pattern.  They work better when you need a more thorough coverage for fungicides and some less common weed killers.

The actual amount of spray applied is a combination of pressure and driving speed. 

****The faster you drive, the less spray will be applied.  The slower you drive, the more spray will be applied. 
****The lower the pressure, the less spray will be applied.  The higher the pressure, the more spray will be applied. 

The owner’s manual for your sprayer will have a chart to help you calibrate your sprayer.