If you're using the Taylor Acid Demand reagent to see how much acid it would take to lower the pH to a certain point, one drop of Acid Demand reagent is equivalent to 9.16 fl. oz. of 31.45 % muriatic acid added to 10,000 gallons.
For your 12,000 gallon pool, 4 drops of acid demand correlates to 44 oz of muriatic acid.
You can use the pool calculator to get an idea of how much that amount of acid would lower the pH. The pH section will be more accurate than the "Effects of adding Chemicals" section.
For example, if you had a TA of 110 ppm and a Borate level of 50 ppm, then going from a pH of 7.4 to a pH of 7.0 would take 45 fluid oz of muriatic and would about equal to 4 drops of acid demand.
However, if your TA were 60, then 4 drops of acid demand would correspond to a starting pH of closer to 7.6.
If you're using the Taylor Base Demand reagent to see how much Sodium carbonate it would take to raise the pH to a certain point, one drop of Base Demand reagent is equivalent to 5.13 oz. (weight) of sodium carbonate added to 10,000 gallons.
For your 12,000 gallon pool, 4 drops of base demand correlates to 24.6 oz weight of sodium carbonate.
You can use the pool calculator to get an idea of how much that amount of base would raise the pH. The pH section will be more accurate than the "Effects of adding Chemicals" section.
Note: The acid demand reagent lowers the sample pH, and the base demand reagent raises the sample pH.
Also, most people can match the pH color within the range of the color chart. Using an acid or base demand reagent will probably not be worthwhile, or helpful. It will probably make things unnecessarily complicated.
You might want to get a second opinion from another person if you are having trouble discerning the color. However, it's important to match the color immediately as the pH can drift if the sample is left too long.