how do I convert an object id to a number

[KristineKosnik]

I need to convert the FID to a number in field calculator.

[JoeBorgione · Accepted solution]

FID = shapefile.  OID = feature class.

Both are internally managed by ArcGIS, so you can't edit them.  They are numbers by the way;  you can add a long integer field and calc it to equal the FID or OID, but not the other way around.

[ChrisDonohue__GISP]

Visuals for the solution jborgion  offered:

Chris Donohue, GISP