alert with thold when cisco switch has %memory used > 80%

[duyenngv]

I try to setup thold to alert though email when cisco switch has %memory used > 80%.
I get memory free and total memory by using two custom SNMP oid,
I can display % memory used by use cdef = (total_mem-free_mem)/total_mem*100
but when I try to setup thold alert, I use RPN expression, I see I only get |ds:total_mem| or |ds:free_mem|. Although, I try to put both total_mem and free_mem in RPN
Pls help me check this problem.

[duyenngv]

After a month, I try to setup Cacti. I think I have to change to other monitor software because Cacti is lacking of email alert option.
It seem I cant setup to alert with two or more OIDs.