Discovery Credit Card calculator updated to include Max Allowable Spend at partner stores

Ok, so I’m using my Discovery Credit Card quite a lot now and getting up to 20% cashback on partner stores but I’ve recently hit my limits – what with all those purchases of iPad 2’s and MacBook Pro laptops!
I knew about the 30% rule which meant that I needed to make the Discovery Credit Card my primary card that I use (“Your maximum discountable spend at partner stores is limited to 30% of your total DiscoveryCard spend in that statement period”).
But, I got a surprise when reading the details about the total limit per month:  “the total cash back is limited to R10 000 spend at all DiscoveryCard partner stores”.
Now that wasn’t at all clear to me!  What did that mean?  I figured that if I totalled up the spend at Pick ‘n Pay, Nando’s, Apple iStore, (you get the idea), then this was limited to a total of R10,000 per month. 
But I had to be sure… so I sent off an email to the Discovery Card email address. 
A few days later a detailed response arrived with an example #BrandPlus.

 

Example (actual calculations can be found in HTT’s updated calculator):
Total spend on Discovery card is R30,000 in the month
Discount depends on Vitality level and number of years on that level
 
That makes the maximum discountable spend at a partner stores: R9,000 [=30% of R30,000]

If you spend:

	% off	Discount:
R5,000 at the iStore	20%	1,000
R300 at Nando's	20%	60
R11,000 at Pick 'n Pay	10%	1,100
		2,160	which is R160 over the maximum allowed R2,000

Max discount per statement:
Depending on Vitality level and number of years on that level

Say you have been on Diamond for more than 5 years, then maximum is R2,000 per month

If the sum of the discount at all partner stores is greater than the maximum discount calculated in the table, then the scaling down factor is applied to bring the total discount in line with the maximum discount.

Scaling Down Factor = 2,000/2,160 = 0.925925926

Then multiply each of the cash back amounts by this ratio which results in proportion value. The proportion value is what is reflected on your statement:

If you spend:	% off	Discount:	Scaled down discount
R5,000 at the iStore	20%	1,000	925.93
R300 at Nando's	20%	60	55.56
R11,000 at Pick 'n Pay	10%	1,100	1,018.52
		2,160	R 2,000.00	which is now equal to the maximum allowed R2,000

These calculations are available in HTT’s updated “Discovery Credit Card Calculator 2011” and can be downloaded here:  http://www.mediafire.com/file/2nc22i2jb4wd1qg/DiscoveryCardCalculator2011.xls

I look forward to your comments to help me make it more understandable and usable.