Read two HX711 load cell amps
The line:
HX711 scale;

is called the &quot;instantiation of the object&quot;. It creates a new object called scale which is an instance of the HX711 class. It is this &quot;object&quot; that is your interface to the HX711 physical device.
To use two of them you first need to have two objects - one for each HX711. You can name them whatever you like.  For example:
HX711 scale1;
HX711 scale2;

The line:
scale.begin(DOUT, CLK);

is where it tells the HX711 object which pins the HX711 chip is connected to. In this case DOUT and CLK which you have defined as 3 and 2 respectively.  You could just as well have written:
scale.begin(3, 2);

Each object has to be &quot;begun&quot;, so you would need a begin for each object you instantiate:
scale1.begin(3, 2); // DOUT = 3, CLK = 2
scale2.begin(5, 4); // DOUT = 5, CLK = 4

Now for every operation that you did on scale you would instead do on your two new objects:
scale1.set_scale(calibration_factor);
scale2.set_scale(calibration_factor);

etc.
And when you want to take a measurement you just select which object to read from:
Serial.print(scale1.get_units(), 1);

or
Serial.print(scale2.get_units(), 1);

You can add a third by creating and using scale3 in exactly the same way as scale1 and scale2.