Re: percentage discount not calculating properly

[Luke <..hidden..>]

On Wed, 24 Feb 2010, Chris Travers wrote:

> This will affect the precision possible, not the method of calculating
> the discount.

Chris

Irrespective of precision from the customer point of view, wouldn't it 
make some sense to do all internal calculations at the highest precision 
available, and only round at the end of, in this case, a line item?

A slightly more complex method, of which I have not fully considered the 
ramifications, is to allow multiple stages of precision rounding.

First stage (inside a line item): maximum precision
Second stage (line total): user specified - higher = more accuracy
	subtotal is based on second stage
	taxes, etc. are calculated on second stage
Third stage (total): user specified - the end result receivable

It may be troublesome to do stages 2 and 3 given taxes, and the things 
we've been talking about re cash based handling of collected sales taxes, 
in which case stage 3 may need to move to stage 2.

I envision it something like this:

[S1] itemprice (imaginary) * discount (imaginary) = 105.04017437
105.04017437 * quantity (5) = 525.20087185
[S2] 525.20087185 round to pre-subtotal precision (3): 525.201
No tax or other subtotal to total modifiers
[S3] total rounded to total precision (2) = 525.20

I have run into companies which do all intra-invoice calculations at 
something like a precision of 4, but then round the subtotal to a 
precision of 2, most likely with a round in their favor (I.E. up).
That's what I'm angling for here.

 > As we revise the invoicing system I would like to be able to handle
> "lot prices" but some additional thought needs to go into how that
> would work.

Add a quantity field to the price matrix, and sort on quantity descending?

Luke