New to access, cannot get total to work correctly

[Big Al]

Forgive me if I am being a total noob or idiot on this.
I am trying to get a sales order form to work correctly without much success
and I am sure its my calculation which is wrong.
I have four relevant columns, one unit price one quantity and one for a
discount and a total price or sales price column
The discount is set up as a percentage format, the other two as currency

In the quantity, say, I put 2 and the unit price is £38.55. for two I apply
a discount in the discount box of 10% this should give me in the sales price
column a figure of £69.39 In fact its giving me a figure of 77.00 i.e. its
taking 10 as a number away from the actual piece price cost (£77.10) instead
of 10%

In the subform text box, for sales price (set up as currency, is this
correct?) the data control source formula in the data expression builder is
=([Quantity]*[unitprice])-[discount]

I am sure this is where its going wrong
Anyone know what the formula should be to give me basically quantity x unit
price - percentage = sales price?

many thanks in advance.
I also have another calculation problem, but I want to get this one right
first

 

[guido via AccessMonster.com]

if the discount value is .1 (10%):
[Quantity]*[unitprice]*(1-[discount])

if the discount value is 10:
[Quantity]*[unitprice]*(1-[discount]/100)

 

[Big Al]

Thanks
Does this mean that I cannot do a rolling change on the order form? i.e 10%
or 20% or other sum on each order?

 

[Big Al]

DHU!!!
Told you I was an idiot!
Ignore the post below. Of course the1 does not change, that's the whole
number
I am a plank sometimes :-0

Many thanks for your answer Guido

Thanks
Does this mean that I cannot do a rolling change on the order form? i.e
10% or 20% or other sum on each order?

if the discount value is .1 (10%):
[Quantity]*[unitprice]*(1-[discount])

if the discount value is 10:
[Quantity]*[unitprice]*(1-[discount]/100)