Q:

Real equivalent of terminal resistance

I found in a book a scheme representing a terminal connection used in making an ammeter shunt (with the purpose of extending its measuring domain).  
I can't understand what the drawing at b) represents. All those resistances want to model the contact resistances.
Then, the book says that in order to make the measurement more precise, we use a "double terminal", drawn here: 
What do these drawings represent in real life and why are the resistances arranged as in the first picture, at c) (the delta connection)? 

A:

Drawing b) represents a terminal cut in half. Let's say that the white rectangle where R3 and Rs are connected is a nut, then you have one ring terminal lug between R3 and R2, then another one between R2 and R1, and then you have the head of a screw at the other end of R1.
Here the contact between the screw and the nut is considered perfect (rather surprisingly) so R1 is directly connected to R3 and Rs.
The double terminal allows to eliminate some of the parasitic resistors. On current shunt you often find 2 big terminals for the circuit where you measure the current and 2 smaller terminals where you connect your voltmeter:

Likewise, on the SMD shunt resistors you'll find 4 pins, 2 for the main circuit and 2 for the measurement:

