It appears that you are mixing up series resistors, intended for measuring higher voltages, with shunt resistors, intended for measuring higher currents.
The range of a milliammeter may be increased by passing the excess current through a parallel resistor, having a lower resistance value than that of the meter.
The parallel resistor is known as the meter shunt.
Shunt resistance = Meter resistance / (n-1) where 'n' is the number of times by which the full scale reading is to be increased.
For example, the range of a 45 Ω meter may be increased from (0 - 1 mA) to (0 - 10 mA) with the help of a 5 Ω shunt resistor (45 / (10-1) = 5).
In practice, a meter shunt is a conductor that has low resistance and is capable of carrying the maximum current that is to be measured.
Here's a drawing of a high current meter shunt.
Holes for shunt / cable mounting and screws for meter wires are shown.
Shunts are classified, not by their resistance values, but by the voltage drop across them at rated current.
Standard values are 50, 60, 75, 100 and 150 mV to pair them with millivoltmeters having full scale readings 50, 60, 75, 100 and 150 mV but graduated in amperes.