Calcium range = 20 to 520 ppm Ca2+
Add 2 mL of water into a cuvette with a stir-bar.
Add 4 drops of test solution #1
Turn on stir-bar and start measuring
Start adding drops of test solution # 2 until the solution turns blue.
According to instructions, each drop is equivalent to 20 ppm calcium.
Count the number of drops.