Firstly, this circuit is designed to measure very low amplitude signals, on the order of a few millivolts, which is significantly smaller than many other circuits. The circuit also has a very high input impedance, which allows it to pick up these low amplitude signals without significantly affecting the signal. Secondly, the circuit includes a number of different subcircuits that are specifically designed to amplify and filter the ECG signal in different ways. For example, there are high-pass filters that remove any DC offset from the signal, low-pass filters that remove high frequency noise, and differential amplifiers that amplify the difference between two ECG signals to remove common mode noise. Some of the different subcircuits in the ECG circuit include the differential amplifier, the high-pass filter, the low-pass filter, and the gain stage. The differential amplifier amplifies the difference between two ECG signals to remove common mode noise, while the high-pass filter removes any DC offset from the signal. The low-pass filter then removes high frequency noise, and the gain stage amplifies the filtered ECG signal to a level that can be used for diagnosis. The purpose for the gap in the PCB shown at [8:58 min] is likely to