Specifically, section 220.127.116.11.
There is considerable verbiage about syntax variations and "1m" vs. "1M".
As the unit for bs is bytes, it would be simpler to specify bs=1048576,
which will work with all dd variants.
As an aside, it could be pointed out that 1048576 is 1 mebibyte, i.e.
1024 * 1024 bytes (optionally referencing SI prefixes
and IEC binary power prefixes