# Cost Item Numbering

Mandrel gives every cost item a number. You can choose between two different hierarchical numbering systems: decimal and fixed-digit.

Since it is not always possible to convert a number from one system to the other, you cannot change the numbering system once you have begun to create a cost breakdown structure.

# Decimal Numbering System

The decimal system uses numbers separated by decimal points. Typical numbers in this system are:

 Level 1 numbers 1. 2. 3. Level 2 numbers 1.1 2.3 3.5 Level 3 numbers 1.1.1 2.3.4 3.5.1 Level 4 numbers 1.1.1.1 2.3.4.5 3.5.1.7

Up to 32 hierarchy levels can be defined under this system, i.e. decimal numbers can include up to 31 decimal points.

Siblings

Siblings are cost items at the same level whose numbers differ only in the last digit, i.e. after the last decimal point.

1.1.1,  1.1.2,  1.1.3 are a sibling group, but 1.2.1 is not a member of this group.

There can be up to 200 siblings in a group, i.e. individual numbers between the decimal points can be up to 200.

# Fixed-Digit Numbering Systems

The fixed-digit system uses fixed-length integer numbers such as 1230. Each one has the same number of digits. You can use anywhere from 2 to 9 digits.

The number of hierarchy levels is equal to the number of digits. Typical numbers in a 4-digit system are:

 Level 1 numbers 1000 2000 3000 Level 2 numbers 1100 2300 3500 Level 3 numbers 1110 2340 3510 Level 4 numbers 1111 2345 3517

Siblings

No more than 9 siblings can be associated with any one number, e.g. cost item 1230 can have 9 children numbered 1231, 1232 ... 1239, all of which form a sibling group. (The next higher number, 1240, is a sibling of 1230, not a child.)

Changing Digit Length

The number of digits may be increased at a later date, up to a maximum of 9, but may not be decreased. For example, if you run out of numbers with a 4-digit system you may increase it to a 5-digit system, although you cannot subsequently reduce it back to a 4-digit system.