use combobox to fill hidden columns in a datasheet of a subform

I have a datasheet in a subform and have in column 1 a combobox with two columns. I would like to use the value of the hidden second column of the combobox to fill in the third column of the same datasheet. However, if I use me.thirdcol = cmbCombo.column(1) then it takes the same value for all rows in the datasheet. Thank you for any help...
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The simple way to do this is with a join.  Here's a real world example.  You have an Order form.  You choose a customer from a combo.  The Customer Name shows in the combo but you want the customer's address to show on the Order Header also.  The RecordSource for the Order form would join tblOrder to tblCustomer on CustomerID.  If Customer is optional, you would use a left join which would allow you to have Orders without customers.  Then select the additional columns you want to display from tblCustomer and bind them to controls on the form.

Using this technique, you almost always will want to lock all the controls bound to tblCustomer fields because you wouldn't want them to be accidentally updated on the order form.

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