## Jul 16, 2008

### TipHashing

I had a great nerdy idea last night as I was filling out the dinner receipt at a restaurant for a credit card purchase. Most restaurants will give you two receipts: one that the restaurant keeps and one for your own needs. I have no interest in putting a slip of paper trash in my pocket, but have occasionally contemplated doing so to "keep the restaurant honest". If I don't keep the slip, how would I really know if they changed the tip on me before charging my card? And if they know I didn't keep the slip, they could feel pretty comfortable with changing my tip and hoping I didn't notice or care.

My new idea is checksumming my tips. First I compute the dollar amount of the total bill that I want to pay: bill + tip. I do this the normal way: 10%-20% added to the bill. Then, I use the cents portion of the bill as a checksum of the dollar portion. An easy thing to do would always be to make it the same such as \$14.14 or \$27.27, but that is also easy to spot and change by a person. Instead, I do the inverse (\$1 - X) of the dollar portion. So for a \$14 total, I would leave \$14.86 (14 + 86 = 100) or for a \$27 total, I would leave \$27.73 (27 + 73 = 100). If you want smaller numbers, you can subtract the dollars from a smaller sum, maybe 50: \$27.23 (27 + 23 = 50). Now, when I get my credit card bill, I can actually figure out if my checksum matches up. If I see a \$15.86 charge, I sum the components (15 + 86 = 101) and I can see that a dollar was added to my bill. Less likely, but possible, a penny was added to my bill - either way someone was mucking with my bill.

## Jul 8, 2008

### Dance Dance Immolation at the Fire Arts Festival

I forgot one small thing about the fire arts festival. Everyone has their favorite piece of art or part of the show, but for me it was hands down Dance Dance Immolation. What is Dance Dance Immolation you ask? DDI is an adaptation of the arcade-style game of a similar name: Dance Dance Revolution or DDR. You play DDR against an opponent and if you are doing good, flamethrowers blast fire up in the air. Except, when you are doing poorly, flamethrowers shoot you in the face with fire. Not a digital version of you either, the "you can die" physical body part of you. And not a virtual flamethrower, we are talking about the ones that shoot flames, as in fire.

## Jul 6, 2008

### Fire Arts Festival

If you aren't in the SF Bay Area this week, you can stop reading. If you are still with me, I would recommend picking up a camera and checking out the Fire Arts Festival over in Oakland running Wednesday through Saturday. I'll be there Wednesday or Thursday probably, have some other things going on Friday/Saturday nights. If you don't have an allergy to fire, it is fantastic. See the video below:

## Jul 2, 2008

### Electric Cars

Toyota has announced that their new Prius will get 94 MPG on gasoline. We already knew it was going to be a plug-in hybrid as well, which means that short trips can be gas-free. It will supposedly be launched as a 2010 model in late 2009. Who knows if that date will be met.

GM is of course betting the farm on the Chevy Volt, an electric-engine car that has a gas engine which spins up only to recharge the batteries when they are getting low. They are shooting for a release date of 2010 as well, although may miss a little bit. They are counting on building out the next-generation of automotive batteries, and building a car around a battery that doesn't exist yet while building the battery in parallel.

Tesla, the underdog in all of this, has just recently announced that they are going to build a sedan version of their exciting Tesla Roadster. It will be an all-electric (no gasoline engine anywhere) sedan capable of carrying 5 people for 225 miles on a single charge and cost \$60,000 with a \$5,000 CA tax rebate. Still a little high, but the gas savings could offset some of that too.

Any way you look at it, the transportation world is moving to electric very very seriously these days. It seems very exciting.