PropaRuler, Measurement of radio wave propagation

It is an application to measure propagation characteristics of 2.4 GHz band radio waves using BLE (Bluetooth Low Energy).
You need an iPhone for outgoing radio waves and an iPhone for receiving radio waves.
In order to perform the radio wave propagation measurement, a ruler to measure the distance is necessary. Activate this application, press the Transfer button in the 1st Step on the screen, then print out the built-in paper craft data of the dedicated ruler, then cut and paste it.
Next, start this application on the iPhone #1, press the Setup button in 2nd Step on the screen , press the Start button on the BLE radio source screen, then set it as the transmission source. And fix iPhone #1 to the 0 cm position of the exclusive ruler.
Next, start this application on the iPhone #2, press the Scan button in Step 3 on the screen, and search the iPhone #1 set as the radio source in Step 2. When you press the name displayed in the list, the screen for measurement is displayed.
Place the iPhone #2 in front of the exclusive 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 press and hold the screen long.
The screen displaying the measurement result is displayed.
Instruction Video: https://youtu.be/0kG7OvWxxqw