Count data Footer on Datatable

Hello webix,
I have question,
How i can count percent (%) from sumColumn data in Footer ?
I have sumColumn Footer on id “detail_gajipokokbelumapprove_sebelum” and “detail_gajipokokbelumapprove_sesudah”

example :
2400000 / 2000000 = 1.2

I want to place value “1.2” on footer id “detail_gajipokokbelumapprove_presentase”

Sample :
https://snippet.webix.com/ou7felnb >> on Menu “Dashboard”

Thank You