I want to calculate phytase activity.The data I have is:

1 - absorbed data

2 - standard phosphate solution absorbed

The way that i use is

I plot a graph with the standard phosphate concentration data which is read with a spectrophotometer and this graph gives me an equation.

I put the absorbed data in this equation and multiplied it by dilution factor and divied by the time of incubation.

Is this a right formula for the calculation of phytase activity? What is the unit of the number which I should gain?