Analog Input. In this example we use a variable resistor (a potentiometer or a photoresistor), we read its value using one analog input of an Arduino or Genuino board and we change the blink rate of the built-in LED accordingly. The resistor's analog value is read as a voltage because this is how the analog inputs work.
For the Haigis formula, the a0 constant moves the power prediction curve up, or down, in much the same way that the SRK/T A-constant. The a1 constant is tied to the measured anterior chamber depth and the a2 constant is tied to the measured axial length.
Again out of this comes the logarithm to base 10 of e, which Huygens calculated to 17 decimal places. However, it appears as the calculation of a constant in his work and is not recognised as the logarithm of a number (so again it is a close call but e remains unrecognised).