DanioScope shows unrealistic low values of heart rate, like 15 BPM. Why ?
DanioScope automatically calculates the heart rate based on changes in the selected section of the video. It analyzes the rate of changes to determine the dominant frequency. Occasionally this can result in an implausibly low calculated heart rate. This is most likely when the video has low contrast, and/or when the heart area defined includes noise, or when a large heart area picks movement unrelated to heart activity. Low contrast enhances this effect by covering the true heart beats.
In this example, the Activity plot is: 
Random noise or irregular movement of blood larger than the average can produce the highest peaks in the figure. The peaks of intermediate amplitude are the true heart beats. You can check this by zooming in the plot. The highest peaks are dominant in the resulting power spectrum plot (see “current results”).
The highest peak, located at a frequency of about 15 BPM, is the reason why DanioScope thinks that the heart rate is 15. Your task, now, is to modify the heart area in such a way it covers only the true movement of the heart.
- Play the video and try to locate the region of the heart which clearly moves.
- Draw the heart area around that region, like in this example.
- Redo acquisition.
Now the power spectrum shows that another peak, around 180 BMP, has become dominant.
This time DanioScope reports a heart rate value of 183 BPM.
You can check the results when you zoom in in the activity plot. A heart rate of 180 should correspond to about 3 peaks per second being clearly displayed in the Activity plot. We recommend to always compare the activity plot with what you see in the video.
Note that this solution does not always work. It is always a good idea to make sure that contrast and sharpness in the video image are optimal in order to improve detection by DanioScope.