[Koha] Koha's call number vs. our library's call number

[Hans Henderson]

As I mentioned in my "hierarchical question" posting, the shelf 
ordering system for one of our book item types (graded readers) is by 
reading difficulty level. 

To accommodate this, I've created an alphanumeric local call number 
unique to each item (copy of a title) I'm also using this as a 
barcode number. the first part of the number shows the level, then 
the set, then the titles, and then the individual copies. So Q010A04 
means "the fourth copy of title A in set 010 at reading difficulty 
level Q".

I plan to put this local call number into Koha's barcode field in the 
items table, and link that field to MARC 852c - please confirm I got 
at least that right, or should I use a 9xx? 

But I see that the *Koha* call number field is numeric. Can we just 
leave the Koha call number field empty? 

I saw Chris Cormack's tip on changing the dewey column's data type to 
varchar within SQL, but messing with the internals at my current 
newbie level makes me a bit nervous. Plus, I will be pulling in 
deweys from many of my MARC records, so where this is so, I'd rather 
store them where they're supposed to go in Koha in case we need that 
data later.

So more to the point, how do we ignore this data in the meantime, and 
use the barcode field everywhere in Koha as a local call number 
field? 

I'd really appreciate some details as to how to do this, as pertains 
to both the opac and the intranet. Or alternatively, I'd also 
appreciate feedback on how I'm totally off-base regarding normal 
library practices <g>, along with suggestions on how to accomplish 
what I'm trying to do.

Thanks,

Hans