Sum across worksheets

This formula returns the sum for the cell in column "A" for each worksheet from Sheet1 to the worksheet where the function resides "=EVALUATE("SUM(Sheet1:"&ShtName&"!A"&Row()&")")+NOW()*0 where ="INDEX(wsNames,ShtPos)" where wsNames is the array of worksheet names in the active workbook and ShtPos = "GET.DOCUMENT(87).