Hi @cs1
Please switch to formula plugin via Handsontable version 1.7.0 (or above) as now it is a proper formula calculations source.
Currently we do not offer multi-table formulas.
If you do not have a lot of cells to fill with the following formula you could use a workaround with instance.getDataAtCell() referring to the other instance’s data. If you could create a draft in the JSFiddle I’d be happy to help.