2. A system consisting of letters may be made more easily mnemonic, each letter being, as a rule, the initial of the term symbolized, and may be recalled to mind more easily than a number arbitrarily chosen for that purpose.
The following example shows how easily a machine can be located and described. If:
- M is used for machine
- L for lathes
- C for core ramming machines
- P for power machines
- R for ramming machines
then:
- ML would immediately suggest a lathe
- MCR a core ramming machine
- MPR a power ramming machine
- Etc.
Where there are several styles of the same type of machine, numerals may be added, as MPR₁, MPR₂, etc.
A combination of these two systems which has been applied to large institutions is characterized by grouping all departments which perform the same class of service under one letter of the alphabet, and then numbering their functions. Frederick A. Parkhurst[72] has outlined a very useful system which may be used in a manufacturing or other plant somewhat as follows. Group A with subdivisions would include:
| 1A Accounting Room | 1B Sales Department |
| 2A Cost Department | 2B Order Department |
| 3A Credit Department | 3B Stenographic Department |
| 4A Billing Department | |
| 5A Filing Department |
Each department of the factory has an arbitrary letter allotted to it and is always referred to in all records by this letter and number.
The Interstate Commerce Commission uses a numerical system of numbering accounts by first grouping each class under “general accounts”; then under each group of general accounts, special accounts called “primary accounts” are numbered consecutively. These accounts have been analyzed so minutely that not much leeway is given for inserting new accounts and for this reason the method is not so elastic as a good classification requires. Thus, Operating Revenue accounts are classified generally into: