A specific internal code change is identified by an Engineering Change (EC) number and a change level.
One unit of internal code is called an Engineering Change (EC). An EC is referred to also as a stream.
An Engineering Change (EC) number is assigned to an EC by IBM Product Engineering. The number identifies the purpose of the internal code in the EC.
An internal code change for an EC changes all or part of the internal code in it. Both an EC and its internal code changes are identified by the same EC number.
But the EC number of an internal code change is qualified by another number, called an internal code change level, to distinguish it from the EC it changes.
The internal code change level, referred to also as a change level, also distinguishes an internal code change from previous and subsequent changes for the same EC.
Example
For example, a unit of internal code, or EC, initially stored on the Hardware Management Console by IBM during manufacturing is assigned the EC number: E01234.
After IBM delivers and installs the console, it may be necessary to change EC E01234 to add new functions, improve existing functions, or correct problems. To do that, IBM provides an internal code change for the EC.
The EC number of the first internal code change would be E01234, while its change level would be 001. The change level would be increased by 1 for each subsequent internal code change for EC E01234.