What is the universal (world wide) understanding behind degaussing harddisks?

[Turritopsis Dohrnii Teo En Ming]

Good evening from Singapore!

The foremost question which I want to ask is, what is the universal
(world wide) understanding behind degaussing hard drives?

I work for No Secrets Agency (NSA) Pte Ltd (fictitious company name
used). My sales manager Edward Joseph Snowden (fictitious individual
name used) had *promised* our customer Leave Me in the Lurch (S) Pte
Ltd (fictitious company name used) that we would "DEGAUSS" their hard
disks after the PC replacement and data migration exercise for 15
trillion PCs (fictitious number used).

PC = Personal Computer, which includes desktops and laptops

Last Friday, I had already reflected to my sales manager Edward
Snowden that since we are definitely NOT going to wipe our customer's
data by using strong and powerful magnets (physical means), should I
send an email to the IT Administrator of our customer Lady Gaga
(fictitious individual name used) asking her which data sanitization
method (by software means) I should use? My sales manager Edward
Snowden had quickly deflected my concerns (that is, wanting to send an
email to our customer Lady Gaga asking her which data sanitization
method I should use).

I had brought up to the sales manager Edward Snowden a number of data
wiping methods by software means last Friday.

(1) Very very simple 1-pass data wiping, quickest

a. Using "sudo dd if=/dev/zero of=/dev/sda", overwriting harddisks
from beginning to end with zeroes, where /dev/sda refers to the 500 GB
harddisk, not /dev/loop0 and not /dev/sdb which refers to the bootable
live operating system on thumb drive

b. Using "sudo dd if=/dev/urandom of=/dev/sda", overwriting harddisks
from beginning to end with random data, where /dev/sda refers to the
500 GB harddisk, not /dev/loop0 and not /dev/sdb which refers to the
bootable live operating system on thumb drive

Any bootable Live CD/DVD/flash media could do it.

(2) 3-pass U.S. Government/Department of Defense (DoD) standard (DoD 5220.22-M)

Certified commercial software required

(3) 7-pass U.S. Government/Department of Defense (DoD) standard (DoD 5220.22-M)

Certified commercial software required

(4) 35-pass Gutmann method, slowest

Certified commercial software required

All these was last Friday. In the midst of our argument over the
cellular network "just now", my sales manager Edward Snowden tried to
cover up himself by suddenly and unexpectedly making an excuse that he
had told me last Friday I was supposed to wipe user data only, not the
operating system!

If he had wanted me to wipe user data and retain/keep the Windows
operating system, he should simply have told me to Reset the PC (for
Windows 10 only) or use a =secure File Shredder=! For Windows 7, you
can still wipe user data and preserve the operating system by using
the Recovery Partition. On Lenovo desktops, press and hold F11 when
Windows 7 is starting and reset to factory defaults.

I had advised my sales manager Edward Snowden not to use BIG WORDS
like "degaussing the harddisk" and market to the customer using these
big words. Any person who sees the word "degauss" would have
understood it to mean sanitize *ALL* data on the harddisk straight
away and without question.

Please refer to Figure 1. Exhibit A below for the "degaussing"
instructions communicated to me by my sales manager Edward Snowden.
Please click the link below.

URI: https://i.imgur.com/bGOMyVs.png

Please advise.

Thank you very much.

Regards,

Mr. Turritopsis Dohrnii Teo En Ming
Systems and Network Engineer
Republic of Singapore
2nd April 2018 Monday 9:35 PM Singapore Time GMT+8