A method and apparatus for reducing the effects of noise on a system for measuring physiological parameters, such as, for example, a pulse oximeter. The system provides a compressed air source, a heated water source, a particulate cleaning medium source, and a mixing valve including an air input, a water input, and a particulate cleaning medium input. The printer has an unwind mechanism that accepts and holds web rolls of different widths in center-justified relationship with respect to a print head. This device also excludes COD estimation as required for BOD estimation of waste water.