1. W3C. (1999). Web content accessibility guidelines 1.0. W3C Recommendation. Cambridge, UK: W3C. Retrieved from https://www.w3.org/TR/WAI-WEBCONTENT/
2. Heart rate variability: a review
3. Wavelet Analysis of Cardiac Electrical Activity Signals
4. Bogdanova, G., & Sabev, N. (2017). The first principle in the standard for web accessibility “Web Content Accessibility Guidelines”. In Science Days 2016. USB branch Veliko Tarnovo, Faber.
5. Bogdanova, G., & Sabev, N. (2017). The second principle of operability in the standard for web accessibility WCAG 2.0. XV-National Conference with international participation “Libraries - reading - communications” - Digital conversion of literary and cultural heritage, 302-314.