Guidelines and best practices
HRV4Biofeedback's unique camera based measurement was scientifically validated and showed to be equivalent to chest strap measurements (Polar H7) as well as electrocardiography.
Make sure to follow these guidelines for all your measurements:
As first time users, try to take 2-3 measurements following the advice above, and you should be able to acquire high quality data rather easily.
Make sure to follow these guidelines for all your measurements:
- Make sure the flash turns on. If the flash doesn't turn on, the app won't be able to measure with high accuracy (which is the reason why you cannot measure using an iPad, unless you use a bluetooth sensor). If the flash doesn't turn on and you have an iPhone, go under your iPhone's settings (in your phone, not in the app) and make sure that HRV4Biofeedback is allowed to access your camera
- Make sure to cover the back camera completely. In some phones the flash might be quite far from the camera. Try to cover entirely the camera and also the flash as much as you can, using only one finger. Here you can find more instructions for iPhones with 3 cameras
- Make sure there is limited light (apart from the flash) in the room you are taking the measurement in. Measuring in dark places provides better measurement as natural light does not interfere with our algorithms, while we measure blood flow using light reflection. It should still be possible to measure accurately when there is sunlight, but in case of trouble, you might want to try a darker room
- If you use a phone cover, remove it when taking the measurement
- Place your hand on the camera before tapping the "Start session" button. The app will discard the first few seconds of data regardless, but placing the finger before starting the measurement can still be beneficial during the first few seconds
- Try not to move your finger and not to change the amount of pressure on the camera. Keep your finger still and in a comfortable position. This is the most important point. While we have techniques in place to cope with motion artifacts, movement will most likely mess up your data beyond what can be fixed
- Do not apply excessive pressure, which might impede blood flow and therefore prevent the app from measuring it correctly
- Do not use earphones while measuring (iPhone only). Unfortunately due to some incompatibilities with the techniques we use, it has been reported that the app might freeze if you measure using earphones on iPhones.
As first time users, try to take 2-3 measurements following the advice above, and you should be able to acquire high quality data rather easily.
Which camera should I use?
Regardless of how many cameras your iPhone has, only one camera is the main camera used by the app. In the app, you can figure out really quickly what camera you should use, as you can see the camera view during the measurement. If you see a red dot as below, then you are covering the right camera, because that's your finger