Thanks for this.
Ive created the column called Drills in the eCart object and also created a column called discountAmount.
ive then gone on to creating the calculations as you have stated, replacing the [catagory] with [Drills] the value is to come from a database field called SubCatID which is = 51 for drills.
From this point can you advise. Do i then go into the discounts tab in eCart and create a discount rule? and if so, can you let me know what the process is for this as im not sure how to go about it from here.