Electronic dictionary for interpreting

Hi Everyone,

I just got a job working part-time, on-call as a Spanish interpreter and have yet to go on my first assignment.

I want to get an electronic dictionary in case I need it while on the job. Can anyone recommend a good electronic dictionary, one that would include more specialized terms for social services and medical situations? I would like to have the ability to add terms to the dictionary as well. Please let me know if you have one that you like.

Thanks!

Oxford Superlex is a good option, although it is not specific for medicine.