Marek Sikora Marcin Michalak 0001 Beata Sikora Approximation of a Coal Mass by an Ultrasonic Sensor Using Regression Rules. 345-350 2011 PReMI https://doi.org/10.1007/978-3-642-21786-9_56 conf/premi/2011 db/conf/premi/premi2011.html#SikoraMS11