How is Rank calculated?

In my company's version of JIRA there are three columns that contain the word "rank".

Global Rank, where apparently all new issues have the same value and are meaningless if you change the rank of an issue in the backlog. At some point in time the values were different, but this doesn't happen anymore.

Rank (obsolete), which appears to be an duplicate of Global Rank

Rank, which is a very strange set of values that DO change when changing an issues actual placement within the backlog (e.g. moving something from top to bottom). These are some of the values that are currently shown for Rank:

0|000000:0000000000000a

0|iin1kb

0|iin1k3

0|iin0sq:

What do these values mean? How is it calculated? According to my administrator page these are NOT custom field value. it says this for the field:

Rank LOCKED
Global rank field for JIRA Agile use only.

I care about this because I would like to organize the backlog by Rank (e.g. 1,2,3,....n) and when viewing issues, send an update to JIRA to move an issue to a new Rank location. (e.g. issue that is 99, gets moved to 55).