many sheets - average value

Hi,

I have to many excel sheets and want to calculate the average value for a certain column!
Describe the problem: I have 300 sheets and there is a column in every sheet , from that I want to calculate the average value!

I don't want to open every sheet and calculate the average value for this column! I'm looking for a script, macro or a tool, which help me to do that in one or two steps! I mean: I want to open all sheets or select them and a macro, script or a tool calculate the average value from a column!

Does somebody know a macro, vb scripts or tool for this problem?

Thanks in advance!

best regards,
doc