Need some more clarifications.. I understood that, you need to have different unit of measure for a product. You can cut a 1000m wire into any number of piece but still for any purpose you can use unit 'meter'.
You can use like this:-
-> From Settings==>Warehouse enable Manage different units of measure for products
and enable Invoice products in a different unit of measure than the sales order
-> Now you can manage UOM from this menu:
Warehouse==>Configuration==>Units of Measure
Warehouse==>Configuration==>Units of Measure Categories
-> Now if you got like a product called 'A' you purchase that in meter's and you cut that to specfic number of pieces (or units) and let's assume one piece is 0.5 m (you are selling it in pieces,(if you need you can define new UOM 'piece'))
-> Now go to Product 'A' form and select settings for Sale tab
In Unit Of Measure section select-
Unit of Sale: Units
Unit of Measure -> UOS Coeff : 2
Now you can sell product 'A' by giving number of units too,, it will calculate price according to previous settings.
Let me Know if any query..
It is possible to suggest better solution only if there is better understanding of requirement,, so please add up details....