On-line analysis has been used for monitoring and process control in wastewater treatment for approximately 20 years. The on-line analysis market started with cabinet analysers. Recent developments of in-situ analysers can result in significant installation cost savings, provide direct measurement at the sampling point and require little or no reagents. The new Stip-scan is a recent example of such an in-situ probe which allows the measurement of multiple parameters simultaneously. The measurement technique is based on UV/Vis-spectroscopy and it is possible to measure nitrate, spectral absorbtion coefficient (SAK UV 254). COD, TOC, TS, SV(Sludge Volume) and SVI (Sludge Volume Index) with one simple probe. No chemcals are needed for calibration or operation of the analyser and in addtion functions with little or no maintenance.