The thermocouples and some other sensors have an output that is non-linear. That means the mV generated by them are not in direct proportion to the parameter measured. In signal conditioning Linearization can be done with cmos fet switches or even comparators and diodes.
In Embedded Systems Linearization is done with Look-Up tables on ROM and also using Math and Formulae for each segment.
The above circuit used diodes and opamps to change the gain for each segment of the curve to make it a straight line within an acuuracy of 1% or 2 %.
LM346 has programmable gain and 4 opamps in one package. The LF442 is a dual low power operational amplifier and superior for DC application in comparison to LM358.
The about configuration increases or decreases the gain of the block. You can use each opamp and the dip-switch to change the gain. The resistor selection is important for obtaining the right gain.