"R1 and R3 should be about 1000 times greater than shunt resistance."
That would be R1 and R2.

Indeed R1 and R2, you are right.

Good clarification Kai.

Thank you.

Kais circuit goes for very high precision, my experience with 4-20 is that such does not exist and for that reason I would not go through the expense of .1% resistors, just 1% will do.

I wanted to offer an alternative to RCV420, which typically yields 94dB CMRR (RCV420BG). For achieving similar CMRR a very high precision of according resistors would be necessary. That's why I suggested 0.1% types. But, as you told, in very most cases 1% types are used, because this is a common standard.

Also, I would insert a resistor (5%) at both ends of the 2 potentiometers to make the adjustment of zero and span easier.

Yes, of course. These sections are highly idealized. Even no actual values for trimmers are given. I only wanted to focuse the differential amplifier section, and I didn't want to give a ready solution. This should be the job of original poster...

One additional hint to Satish: When a trimmer is used, keep in mind, that wiper terminal needs a minimum load for preventing contact problems. This interesting advice a technical advisor of a trimmer producing company gave me, some years ago. If only nanoamperes or even picoamperes are flowing, contact problems are probable, especially, when wiper is only one time set, like with a typical calibration routine, and is 'forgotten' afterwards. So, just connect 100k resistor or something like that from wiper terminal to ground. A current of at least 1µA should flow, as a rule of thumb.

Kai