How to create trigger to sum a field?

[praise1234]

Hey there,
I need to create a trigger to sum a field everytime. This total field will be adding up field1+field2, and the value of field1 and field2 is dynamic, input from the users on the fly. Any help is appreciated.
Thanks a lot.

 

[lewisp]

key-nxtitm perhaps, so that the value is calculated when the user hits RETURN?

 

[praise1234]

Yes. Once the user enter the value for field1 and field2, the total field has to adding up the field1 and field2 value and return the total value in the total field when they hit Return.