Switches represents binary input, MSB is on top (most left bit in binary number, most significant bit), and LSB is on bottom. With 5.33kohm resistor we can set maximum value of analog output with following equation Av(amplification)= (Resistance between output and - input divided by parallel resistance of input resistances) and in this case Av is 1.If we multiply input voltage with Av we can get maximum output voltage. With switches we add voltages to - input and every switch adds different amount of voltage (Because this is 4 bit DAC maximum binary value we can convert is 1111 or 15 in decimal so binary value on input dovided by 15 and multiplied by Av is value on output, LSB adds Av*Vin/15=0.333V, second bit is decimal 2 so Av*2*Vin/15, third bit adds Av*4*Vin/15 and MSB or fourth bit adds Av*8*Vin/15.) If we set bit 2 and bit 3 to 1 and others to 0 we can calculate output voltage by adding output voltages for that two bits from previous sentence.
