SoundPRuler, measurment of sound wave propagation

This is an application to measure propagation characteristics of acoustic waves.
You need two iPhones. iPhone#1 for a sound source and iPhone#2 for a sound receiver.
In order to perform sound propagation measurement, a ruler to measure the distance is required. Start up this application, in the 1st Step on the screen, press the Transfer button, print a paper craft data of the ruler with the printer, and please cut and paste it.
Next, start up this application on the iPhone#1, in the 2nd Step on the screen, press the Setup button, and set the frequency of the sound source. Then connect an external speaker to this iPhone and place the L side of the external speaker at the corresponding to the 0 cm position of the ruler.
And press Start button, then the sound of the set frequency will come out. Please adjust the volume if necessary.
Next, start this application on the iPhone #2, in 3rd Step on the screen, press Setup button and set iPhone#2 in front of the ruler of 0 cm. At this time, please keep the iPhone#2 about 10 cm above the ruler by using a spacer, so that the scale mark of the ruler is the same length as the cursor displayed as "- 1 ------- ▽".
Touch the screen to start measurement. When moving the iPhone and the cursor crosses the ruler's graduation line, the display will be "0 ------- ||". When the indication is "||", please do not move the iPhone as it is measuring the radio field intensity at that position. When the display changes to "▽", move the iPhone, stop the cursor when it crosses the next graduation line and the display changes to "||". Measurement of the next position will start. The number on the left represents the distance traveled.
Repeat this operation for the distance necessary for measurement.
After measuring the required distance, please long-press. The measurement result is displayed on the screen. Save the plot image to the photo album with Save button.
Caution:
· Please be aware that an external speaker may be very loud and may be dangerous.
· Built-in iPhone speaker is not possible for the measurement . Please use an external speaker..
Instruction Video https://youtu.be/CaHObe6g-_E