To better understand this section, it is suggested that you first read:  Conditional Actions – Explained and Accessibility

The Compute Value Conditional Action allows a User to build an assortment of arithmetic operations with a variety of operands.

You do not need a trigger field to fire a compute button.  The calculation will fire always on save or if you hit the calculator icon next to the field to be computed. See Fig 2 for example of a calculator for the TrialKit web.

1) When a user selects the Conditional Action type Compute Value

2) A dialog box opens at the bottom of the Conditional Actions Builder as shown in the figure below.

The example below is a compute for age
Fig 1

Operators are as follow:

+ = Addition

- = Subtraction

* = Multiply

/ = Divide

, = Comma (operator)

BMI Sample Formula:

Formula: weight (lb) / [height (in)]2 x 703

Calculate BMI by dividing weight in pounds (lbs) by height in inches (in) squared and multiplying by a conversion factor of 703.

Example: Weight = 220 lbs, Height = 6’0″ (72″)
Calculation: [220 ÷ (72)2] x 703 = 29.8

Fig 2

TrialKit web example of BMI calculation

TrialKit application example of BMI calculation

Another way is to do a scoring field on the web is to add up the fields as shown below in Fig 3 below:

The condition will look like Fig 4 below: Notice how there are no trigger fields used.  The calculator next to the field will compute or on save of form it will always compute.