“…Words per minute (WPM) (Arif and Stuerzlinger, 2013), , (Faraj et al, 2009c), (Faraj et al, 2009a), (Faraj et al, 2009b), (Ghosh, 2011), (Gizatdinova et al, 2012a), (Guerrier et al, 2011), (Hoste and Signer, 2013), (Jain and Bhattacharya, 2010), (Joshi et al, 2011), (Miró-Borrás and Bernabeu-Soler, 2009), (Molina et al, 2009a), (Molina et al, 2009b), (Nicolau et al, 2013), (Panwar et al, 2012), (Sarafis and Markoulidis, 2010), , (Sharma et al, 2012), (Topal et al, 2012), (Vella and Vigouroux, 2013) Characters per minute (CPM) (Bhattacharya and Laha, 2012), (Burgbacher and Hinrichs, 2014), (Polácek et al, 2012) Gestures per character (GPC) (Polácek et al, 2012) Keystrokes per character (KSPC) (Miró-Borrás and Bernabeu-Soler, 2009), (Molina et al, 2009a), , (Wu et al, 2014) Total error rate (TER) (Arif and Stuerzlinger, 2013), (Biolchini et al, 2007) Minimum string distance (MSD) (Gizatdinova et al, 2012a), (Nicolau et al, 2013) use four keys. The number of keys may increase, but is limited to the number of symbols in the alphabet.…”