1. Gartner, Inc. Forecasts that 20.4 Billion Connected Things Will Be in Use Worldwide in 2020
https://www.gartner.com/en/newsroom/press-releases/2017-02-07-gartner-says-8-billion-connected-things-will-be-in-use-in-2017-up-31-percent-from-2016
2. State of the IoT 2018: Number of IoT Devices
https://iot-analytics.com/state-of-the-iot-update-q1-q2-2018-number-of-iot-devices-now-7b/
3. Internet of Things Statistics 2019 [The Rise of IoT]
https://techjury.net/stats-about/internet-of-things-statistics/
4. 2018 Roundup of Internet of Things Forecasts and Market Estimates
https://www.forbes.com/sites/louiscolumbus/2018/12/13/2018-roundup-of-internet-of-things-forecasts-and-market-estimates/
5. Fundamentals of Quartz Oscillators, Application. Note 200-2
Leapsecond.com/hpan/an200-2.pdf