Create a formula for two fields that do not block each out

Seeking help on creating two formulas that do not cancel each other. I can create a formula for each of the two fields, separately, but they no longer work when both formulas are in place. These are the two formulas I am currently working with. After entering the current rate, I would like the option of either entering the percentage to calculate the new rate OR after adding the new rate it calculates the percentage.

                                           Current                                New

                                                     Increase

First formula is to show the percentage between the current and new pay rates:

var a = Number(this.getField("New").valueAsString);
var b = Number(this.getField("Current").valueAsString);
if(b)
event.value = ((a-b)/b)*1;
else
event.value = "";

Second formula is to calculate the new pay rate based on current rate and increase percentage:

var b = this.getField("Current").value;

var c = this.getField("Increase").value;

var newPayRate = currentPayRate * (1 + increasePercentage / 100); event.value = newPayRate.toFixed(2);