AccelaRuler FAQ

How do I achieve the best accuracy?
With proper technique, you should typically get results within 2% of the actual distance. There are three factors of prime importance:

• Speed/acceleration. Faster is usually better. An accelerometer loves to accelerate -- use it!

• Motion at the end points. The algorithm used to compute distance relies on the fact that the device is stationary when you press the button at the end points. More motion == more error.

• Changes in tilt. Gravity affects the acceleration measurements, and the relative direction of gravity changes when the device is tilted. Keep the device as level as possible - typically flat on a table or other surface.

Other tips

• Original iPhones and the iPod Touch work great with AccelaRuler. Owners of the 3G iPhone need to be bit more careful while measuring since the phone’s rounded back can allow the device to wobble, upsetting the measurements.

• Sharp accelerations resulting from bumping into objects will cause measurement errors. Try to keep all movements smooth.

• Make sure that your device is absolutely motionless while recalibrating.

• Letting the device sit motionless for a second or two between measurements will allow the automatic self-calibration to work better.

• Manufacturing tolerances. Accuracy testing was done on multiple devices without issues, but it’s possible that there are some accelerometers out there that don’t behave the way that AccelaRuler expects. Let us know at support@wakaware.com.
Still doesn’t work for me. Now what?
Try the following:
• Leave device motionless for 3 seconds.
• Without moving it at all, tap the “Start measuring” + ”Device is at point A” + “Device is at point B” buttons as quickly as you can. The device should read 2.5 inches, or something very close to that. If not, let us know at support@wakaware.com.

Assuming that works well, take the device to a countertop or table where you have a clear, smooth path of about 4 feet (1.2 meters). Often it’s easiest to learn to use AccelaRuler at this distance before proceeding to measure shorter or longer distances.

Try to measure the distance, taking about two seconds to slide the device one way and another two seconds to slide the device back to the starting point. Follow the on-screen tips, if any, and try this test several times until you get measurements in the green on the quality meter. At that point, the measurements displayed should be close to the true distance, typically within the plus or minus amount shown.

Also see the answer below on how to use the accelerometer tuning mode.
When do I need to Zero Reset?
AccelaRuler continuously self-zeroes when you aren’t actively measuring. A Zero Reset is really only required for major orientation changes, such as moving from measuring a table to measuring something vertically on a wall. Of course, if your readings are way off, go ahead and tap the Zero Reset button. Remember that it is critical that the device not move at all while zeroing.
How does the accelerometer tuning mode work?
Starting in AccelaRuler version 1.1 there is an accuracy enhancement feature that allows you to tune the measurements more closely to your specific movement patterns. This is not meant to be a frequent or even necessary operation, but it can improve accuracy once you are comfortable using AccelaRuler.
In a nutshell, you enter Tune Mode by tapping the “Tune Accelerometer” button on the back side info screen. This automatically takes you back to the measuring screen which asks you to repeatedly measure a 14 inch (36 cm) length, such as the width of a MacBook Pro.
The key to a successful tune is to repeatedly and very consistently measure the 14 inch (36 cm) distance. The tuning algorithm will monitor each measurement pass, and if it within the tolerances, use it to adjust trimming coefficients in the measuring algorithm.
At the end of the series of measurements, the info area will tell you whether the tuning completed successfully or not and show you the calculated coefficients with the number of successful measurement passes used in parenthesis. A minimum of 6 successful passes are required for each value to be considered a successful tune. If it was successful, the results are saved and used for future measuring. If it wasn’t successful, the results are still shown but are not saved.
Typical coefficient numbers will range from 0.25 to 0.45 for the first value, and 0.60 to 0.90 for the second. Even if tuning is not successful, you can compare the results to what AccelaRuler is using. If the values are within +- 0.05, then you won’t notice much difference even if the tune completes successfully.
I obviously only have a limited selection of devices to test with, so if you complete a successful tune, it would be great if you could send a note to support@wakaware.com with your tuning values!
Can I measure distances while walking around?
AccelaRuler is really only meant to be used on flat surfaces. Of course, feel free to experiment with this by carrying the device sideways. Remember that the device measures forward and backward along the short side, not in the “natural” carrying position aligned with the long axis of the device.
Do I have to follow the on-screen arrows when I slide the device?
No, both directions work the same way.
Can I measure vertically?
Yes. Calibrate first by placing the device in the orientation that you want to measure and pressing the “Recalibrate” button. Remember to hold the device absolutely stationary during calibration.

How does AccelaRuler work?
Warning: nerd speak ahead. AccelaRuler samples the accelerometer data stream several hundred times per second. AccelaRuler then applies a simplified form of a Kalman Filter known as an alpha-beta-gamma filter to estimate and correct out errors in the raw accelerometer data and produce position information.

I’m a contractor building a house. Should I throw away my tape measure and just use AccelaRuler?
Mmmm...no. But you could certainly use AccelaRuler as a convenient way to get length and measurement estimates of any number of things around the job site.
I read the FAQ and I still have questions. Who do I contact?
Email support@wakaware.com

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