The particular methodology used in this Demonstration is called dual slope; for a long time this was the primary mode of analog-to-digital conversion. Dual slope operates by using an integrator circuit to integrate the voltage signal for a specific length of time () and then integrate a reference voltage (±5 V) to get a linear slope toward 0 V, recording the amount of time it takes to get to 0 V from the first integration. The integration of the constant voltage creates a linear voltage ramp toward 0 V, so by recording the time it takes to get to 0 V from the last part of the integration of the signal, it gives you a value proportional to the top part of the integration of the signal (as with a linear voltage ramp, time is proportional to voltage). Although this gives you a time proportional to the voltage of the integration (because the first integration is for a constant duration every time and is relatively short), it also gives a value relatively proportional to the signal ().

In this Demonstration, the parts of the sine wave () that are integrated and the voltage created from the first integration itself are in red, and the constant slope downward is in blue.

The first integration goes from 0 V to some voltage () after integrating the voltage signal for a specific amount of time, then the second integration goes from that voltage () to 0 V with a constant, linear slope and records/outputs the length of time it takes to reach 0 V from .

The formula for how an op-amp integrator circuit works is , where is the resistance and is the capacitance. Integrating a constant voltage gives . Only a single-input signal is considered.