Measuring the GFP expression is a useful tool worldwide for quantifying gene expression. Currently, there are various differences in fluorescence data which is measured on different devices (e.g. different units of fluorescence recorded or different settings of the data processing used). The aim of the Fifth InterLab study is to make fluorescence measurements more compatible among various laboratories around the world. This is to be done by standardising the protocol for the machine calibration with Silica beads and relating OD600 values with colony forming units (CFUs). The expression of the GFP by one cell will be calculated by dividing the fluorescence of a population of cells via CFUs instead of using an OD600 measurement which is less precise.