Tag Archive: tip

Have worked on Android for almost a year, we are expanding to Apple’s iPhone market as planned. We decided to port Advanced Tip Calculator over from Android to iPhone as our first app. It will be a free app that has the full feature of the paid app Advanced Tip Calculator on Android. I have to say, the experience working on the two platforms are totally different. Good news is Apple finally approved this app after a week waiting. It is live on app store now.

Here are  some screenshots.

And here is the link to the iTune store.



Admit it, as a developer, we all assume tip calculator is simple. There are probably hundreds of tip calculator apps on Android and iPhone. We made our tip calculator app simply because it is a good app to start. We have a new design of this app a couple of months ago.  It looks cool and very functional. I thought we are done with it, until one day, a guy named Sean left a comment on our app, saying “Can’t add 9.95+1.00(=10.94?) 10% tip”. I didn’t really pay much attention until I grab my tipcal app and did exactly what Sean said. I entered 9.95 as the bill, adjusted tip percentage to 10%, the app shows $1 as tip but the total is 10.94 which is wrong.

My first thought is it is a rounding error. After debugging, I realized it is not the case. 10% of 9.95 is 0.995, so total should be 9.95 + 0.995 = 10.945. If it rounds, it should still be 10.95, not 10.94. It turned out the root reason is when doing 9.95 + 0.995 in computer word, the result is 10.944999999999999. After rounding it becomes 10.94, not 10.95 as expected.

I downloaded a few other popular tip cal apps, on Android and on iPhone. To my surprise, all of them have the same error. See below. It is very common for developers to do it this way. We were trained to keep the precision at the maximum during the intermediate steps and only round at the final step. That’s why all apps have the same error. However from user point of view, 9.95 + 1 = 10.94 is wrong. Even it is just one cent difference, developers have no excuse for it.

And here is our tip cal app after fixing the bug. Thanks Sean.

Post updates for all the tools

I just post updates to pretty much all the Advanced tools apps on Android market. The main fixes are
1. Fixed camera preview not working on Samsung Galaxy S phones. It affected Advanced Bubble Level Pro, Advanced Ruler Pro, Advanced Protractor Pro
2. Added market licensing checking to all paid apps
3. Use ProGuard to obfuscate all the apks to protect our copyright
4. Made no sounds by default in several apps as people complained the sounds are annoying.
5. Phone database updates for Ruler and Ruler Pro


The previous Advanced Tip Calculator is simply an extracted version from the Advanced Financial Calculator. It doesn’t have a good usability. So I redesigned the tip calculator over the weekend and release it as donationware. There are both free-ads-support version “Tip Calculator Donation Free” and paid version “Tip Calculator Donation”. The ads revenue and sales revenue from both  apps will be COMPLETELY donated to some non-profit/charity organizations to help people in need (such as fighting with AIDS or cancer, post-catastrophe reliefs, helping people in poor countries). And I will post receipts with the amount when it happens.

It was a great day today. Just in one day, we sold 27 copies of apps. For many other popular apps, this number is way too small. But for us, it was a great improvement. Most of the sold apps are Advanced Ruler Pro because we just released an minor update this morning. As the only camera ruler on the Android market, it certainly has the advantage.

Starting with the first app Advanced Financial Calculators, it was a bumpy ride to sell on Android market. The Android market is much less mature than Apple store. The infrastructure is not very good. Developers cannot even view their own paid apps’ comments if they are using a dev phone. No real-time statistics update, no reporting tool, no proper way to response to users’ comments, 325 chars limitation to app description. And the most importantly, the market size is much less than Apple store. After a few days after I realized the reality, I treated the dev. work as doing something fun rather than making money. However, I do have a believe that one day Android market will pass the Apple store because of the openness of Android platform, just like PC passed Mac many years ago. That’s when Android developers can really seriously make money.

I also want you know, the sales from all our apps till the day before yesterday (about two month period), excluding the 30% taken by Google, has been donated to Jet Li One Foundation which will be handed over to the victims of China Yushu Earthquake, a 7.1 earthquake with a stunning death toll of more than 2200, leaving thousands of people homeless in an extremely cold place. Those people need the money most. You can find a receipt below. I covered the amount as I am not ready to disclose how much sales we made so far. But if you purchased our apps in the past 60 days, you know that your money is on their way to help people. Let’s wish one day that they can build stronger buildings which will not collapse and innocent students will not be buried.

Looks like there are tons of tip calculators on the android market. Nevertheless since we already did it as part of Advanced Financial Calculator, we extracted it out and made it a free app so that it is available to everyone. What we like about it is that in addition to the tip splitting and rounding features that other tip apps have, it also can save the tips into history and bring it back any time. All previous inputs are remembered so next time to find out the tip, all you need to do is to input the bill total, simple as that. You can even email it to your own email address to keep a record or to your friend to remind he/she owes you some money since you pay the bill this time. It kind of changes from a simple tipping app to a prefect application to keep track of all the dinning expenses. You may want keep an eye on it as you might know already, dinning expense could be huge sometimes.

Here are some screenshots.