It will be a shame if Freebase closes. If it does we will migrate to using Wikidata, DBPedia, or roll our own from the data dump.
The source code should be in the pandora.jar, otherwise you can get it from the SourceForge project.
You do not require the Calculator to do math. Look at the Plus script, or SimpleAddition. They work from first principles, which is more involved, but the real way to go.