Jono-Maybe you can help on this particular question. Why after 3200ISO, does it say 4000pushed,5000pushed and 6400pushed?
jono gave you a peculiar and incomplete answer.
Look at the specs for Nikon and Canon released in recent years, they report separately "ISOs" and "ISOs pushed".
This has a rather specific meaning.
A standard ISO refer to in-sensor adjustable amplification or gain. Push refers to amplification or gain in post processing, after going beyond the maximum the sensor can perform.
for example, 6400 (as a 'pushed' ISO) takes images at 3200 ISO from the standpoint of the sensor. Indeed, it produces the exact same raw file as a 3200 ISO image capture.
all the 6400 ISO setting does it instruct the internal exposure meter (if you even use it) to underexpose by 1 stop, direct the in-camera histogram and back panel rendering to overexpose by 1 stop, and add to the EXIF file an instruction to boost exposure by 1 stop in post-processing (for software that does so automatically when instructed).
What that means, in practice is that the
actual maximum ISO of the M240 hardware is 3200, and the Leica did not disclose this fully in earlier released specifications. by the standards of contemporary digital camera specifications, this was a whopper of an omission by Leica.
In photoshop, you could just as well leave the camera on ISO 3200 underexpose and push the M240's raw file to 4000, 5000, 6400 or -- why stop there -- to 12800, it's no more or less valid a procedure. It's the same procedure.