Marsden is Here

"Use or stack"

Z energy, one of our national service station chains, has a thing with their petrol where if you are a member of a participating loyalty program you can get a small instant discount on a petrol purchase, or you can "stack" the discount and use the aggregate on a later purchase. (I have no idea if other chains have similar deals).

I've been just taking the instant discount, but one sleepless night last week my brain started doing the math.

Ignoring certain constraints (I'll get to those) to get the hang of the numbers:

- if I buy 10L and use my 6c/L discount I will save 60c
- if I do this 5 times I will have saved a total of $3
- if I then make a 50L purchase using the same discount I will save another $3

For a total saving of $6

Alternately:

- if I make 5 purchases (doesn't matter what the volume) and stack that 6c\L each time (saved $0 so far)
- and then make my 50L purchase using my now 36c/L (because I get to add the base for this visit as well) discount
- my saving on this one purchase is $18;

Clearly the optimal approach is to make the maximum number of smallest-possible purchases before making one big one.

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All well and good, I could cheerfully put the minimum amount of fuel I need into my car once a week until I have a big trip ahead or I am up to a free tank. However once you get into the fine print of this particular promotion there are a few more angles.

- Firstly you have to spend at least $40 (before discount) to stack. That's a bit less than 20L at current prices, roughly half a tank or about 2 weeks driving for me under normal circumstances.
- Secondly each stacked portion expires after 50 days (7 weeks) if it has not been used.
- Thirdly the stacked discount only applies to the first 50L of the purchase. My tank holds less than that so for me it's not really a constraint.

So the best I can probably do is

- take advantage of the 10c\L specials which they have every week or so. I don't have a handle on that frequency yet.
- On weeks 1,3 and 5 buy 3x $40 stacking @ 10c\L each time
- On the 7th week fill my tank - about 45L @ 40c\L = $18

That's going to last 4 weeks before we begin the cycle again, so

- 11 week cycles
- into 52 weeks (rounding up because the weeks I drive more will outnumber the weeks I drive less) is 5,
- so over the course of a year that would be savings of $90

Which isn't stunning but is still most of a full tank, or most of a summer month of electricity bills, or a nice dinner out for two.

Those who drive more, or who have more petrol-hungry vehicles (which I hazard to say is still most of the cars on the road), or who are fuelling more than one vehicle on the one rewards card will do better. If

- with a similar tank size
- you are spending $40 every week hopefully stacking 10c\L
- then by week 7 you will be up to 70c\L and saving $31.50 a cycle on only 9 week cycles
- rounding up to 6 of those in a year brings us to $189.

Which still may not seem a lot, depending on your financial situation. Divided by the time spent visiting the pump it's probably not a bad return on the effort.

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You can see the effect of more stacks more clearly by looking at the amount saved as a percentage. I'm calling the full tank spend $100 because the last few fills from near-empty I have done have come in one side or the other of that number.

In my case I would have spent ($40 * 3) + $100 a cycle without discount, and have save $18. 18/220 => 8.18%
In the higher-use case ($40 * 6) + $100 sees a saving of $31.50 31.5/340 => 9.26%

Regardless Z Energy is still getting the bulk of the money, and doubtless prices are set to still make a good profit even if all their customers were doing this.

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Incidentally business customers only get 8c/L off, non stacking, and of course there is an account fee which will eat into the savings. I think a small business owner with only one or two vehicles/drivers to manage might well be numerically better off stacking the regular discount. Of course that adds overhead in keeping track of when it's time to "use it" and it all ends up being tax-deductible anyway and hopefully your small business isn't running on margins/cashflow tight enough to mean it would make a significant difference....

Rape Culture 101
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The new, silent, French revolution - Paris trials help-yourself, electrically powered hire cars on the same model as the Paris do-it-yourself bicycle hire scheme.

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The Economy of Ideas written about the issues surrounding digital property sometime in the 90's I believe, issues still not resolved.

Throughout the time I've been groping around cyberspace, an immense, unsolved conundrum has remained at the root of nearly every legal, ethical, governmental, and social vexation to be found in the Virtual World. I refer to the problem of digitized property. The enigma is this: If our property can be infinitely reproduced and instantaneously distributed all over the planet without cost, without our knowledge, without its even leaving our possession, how can we protect it? How are we going to get paid for the work we do with our minds? And, if we can't get paid, what will assure the continued creation and distribution of such work?

Since we don't have a solution to what is a profoundly new kind of challenge, and are apparently unable to delay the galloping digitization of everything not obstinately physical, we are sailing into the future on a sinking ship.

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Personal names around the world

People who create web forms, databases, or ontologies are often unaware how different people’s names can be in other countries. They build their forms or databases in a way that assumes too much on the part of foreign users. This article will first introduce you to some of the different styles used for personal names, and then some of the possible implications for handling those on the Web.

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