cards instead of stamping, which can facilitate automated processing on machinery not capable of optical character recognition. There are also variations based on manufacture and machine used, and whether the user wants to record weekly or monthly recordings. The time cards usually have the workdays, "time in", and "time out" areas marked on them so that employees can "punch in" or "punch out" in the correct place. The employee may be responsible for lining up the correct area of the card to be punched or stamped. Some time clocks feature a bell or signal relay to alert employees as to a certain time or break. Fraudulent operation of time clocks can include overstamping, where one time is stamped over another, and buddy-punching, where one employee records time for another. In extreme cases, employees can use buddy-punching to skip entire days of work or accumulate additional overtime. Self-calculating machines Self-calculating machines are similar to basic time clocks. Nevertheless, at the end of each period the total time recorded is added up allowing for quicker processing by human resources or payroll. These machines sometimes have other functions such as automatic stamping, dual-colour printing, and automated column shift. Software based time and attendance systems are similar to paper-based systems, but they rely on computers and check-in terminals. They are backed up with software that can be integrated with the human resources department and in some cases payroll software. These types of systems are becoming more popular but due to high initial costs they are usually only adopted by large business of over 30 employees. Despite this they can save a business a lot of money every year by cutting down errors and reducing administration time. Mobile time tracking With the mass market proliferation of mobile devices (smart phones, handheld devices), new types of self-calculating time tracking systems have been invented which allow a mobile workforce – such as painting companies or construction companies - to track employees 'on' and 'off' hours. This is generally accomplished through either a mobile application, or an IVR based phone call in system. Using a mobile device allows enterprises to better validate that their employees or suppliers are physically 'clocking in' at a specific location using the GPS functionality of a mobile phone for extra validation. Biometrics Biometric time clocks are a feature of more advanced time and attendance systems. Rather than using a key, code or chip