[How to build a millivolt signal conditioning circuit with compensation?]

I want to build a miniature circuit which perform the following functions

1.Measure a voltage signal between 0-20 millivolt DC signal

2.Measure a  voltage signal between 0-24 V DC signal

3.Calculating a compensation factor as K = a Constant/voltage measured at step2

4. Multiply the compensation factor K with millivolt signal of step1

5.Transmit value got in step4 as standard 4-20Ma[500 Ohm] /RS485  signals

I want the circuit to be made on a single board with ICs [as tiny as possible].

Thank you.