add cell a to cell b on worksheet ( both cells linked to other cel
 

example: add cell g12(gas) to g13(oil) on worksheet (year 2005). cell g12
linked to another worksheet (h15 gas june 2005) in workbook, cell g13 linked
to(h16 oil june 2005). when add (copy paste etc) sums link june2005!h16 (g13)
with g12 not link (june2005!h15).
any help appreciated greatly