<font face="Verdana, Arial, Helvetica" size="2">As an example consider a 400' minima on a Non Precision Approach at an elevation of 2000' and an OAT at the field of -15 deg C.
4 x (-26x2) = -208'
So what would the true altitude be if you flew to the minima with no correction ? SCARY HUH ! So you apply that correction AND set 400' on your RADALT and when you get to that minima of 608' INDICATED ALTITUDE your RADALT will say 400' AGL(assuming flat terrain).</font>
Providing you have an altimeter setting that was measured at the airport in question, the correction would be
4 x (-26x0.4) = -41'
That's because...
<font face="Verdana, Arial, Helvetica" size="2">Your faithfull Baro Altimeter measures the difference in air pressure between MSL and the altitude you are flying at...</font>
...it actually measures the difference in air pressure between
the station at which the altimeter setting was measured and the altitude you are flying at.
The station was at 2000 ft at the airport, the MDA is at 2400 ft, so the column of air to which the temperature correction applies is only 400 ft high.
(Flying NPAs into airports at high elevation with no weather reporting facilities is, of course, a different matter, and asking for trouble!)