# Re: percentage discount not calculating properly

• Subject: Re: percentage discount not calculating properly
• From: Luke <..hidden..>
• Date: Wed, 24 Feb 2010 15:11:48 -0500 (EST)

```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

```