"Good coffee deserves good brewing."
    - Donald Schoenholt, Gillies Coffee, NY

It used to be that the only quality control method for brewed coffee was tasting it.  It's of course still true that the finished product has to taste good in the cup, but an objective analysis of your brewed coffee can help tremendously in figuring out just what's wrong.  

To use the SCAA brew control chart below, you need three basic measurements -- volume of water used, weight of coffee used, and strength of the brewed coffee -- and then plot these to determine the extraction.  

A complete brew analysis includes also the temperature of the brew water and how long the water is in contact with the coffee, and assessments of the way the coffee is ground, bed depth of ground coffee in the brew basket, and how well the spray head is wetting the grounds.

The objective of course is get into the 'Optimum Balance' area.  Way back in the 1950's, the Coffee Brewing Institute, under the direction of Prof E. E. Lockhart at MIT, determined -- by asking a lot of coffee drinkers their preferences -- that there was indeed an optimum balance of extraction and strength.  The SCAA has repeated this survey at their annual conference and confirmed the people's preference is still about the same today, at least if you're American and the coffee is roasted medium.  There is a difference for dark roasted coffee -- it tastes stronger than medium roast -- and Europeans like stronger coffee (but at the same extraction). 

How the chart works

Here, 'strength' means how much of the coffee beverage is actually coffee, so 1.25 on the scale above indicates that 1.25% of what you're drinking are coffee solids dissolved in the water.  'Extraction' means what fraction of the original dry ground coffee has ended up in your cup.  For example, if you start with 5 oz of ground coffee, and 1 oz dissolves during brewing, then the extraction is 1/5 or 20%.  The red diagonal lines show how much coffee you started with -- for example, the line labeled 3.75oz (106 grams) means you put that much ground coffee into the brew basket.  On this particular chart, the brewing formula always assumes 1/2 gal (1.9 liters) of hot water with each coffee weight.

For the algebraically inclined, the calculations assume that about 1.5 oz of water will remain in the ground coffee after brewing.  So if you start with 4oz of ground coffee, pour 1/2 gallon of hot water over it, and measure the strength to be 1300 ppm, then the extraction is just

{[64oz water - (4oz coffee x 1.5oz water/oz coffee)] x .0013}/4oz coffee~ 19% extraction

Remember that the brew chart applies to the actual amount of water you pour over the coffee grounds.  If you want to end up with 64oz of brewed beverage, you'll need to start with more water -- about 70 oz in this case.  To maintain the 4oz/half gallon ratio, you would need to increase the weight of coffee to 70/64 * 4oz = 4.37 oz.