ee1874

On positive of input, what use for the chooice of different path of resistor? Why the first resistor is 10ohm, then suddenly to 1k ohm and suddenly to 100kohm? Why not use 10k ohm for second and 1k ohm for first? How to know the 10ohm is for range 200mV and same for 1k,100K,1M,10M, how to know their voltage range? Got formula to calculate it? On negative of input, what use for the adjustable resistor ? Can eplain more detail about the function of the ajustable resistor? Can explain whole circuit to me?