The present invention relates to a method for evaluating the start of an assay in a fluidic chamber, wherein said start of the assay is based on the dissolving of a reagent in a region of interest in said fluidic chamber. The method may be based on the detection of an optical effect in the region of interest caused by the dissolving of the reagent, comprising the steps: obtaining an optical signal from one or more sub-sections of said region of interest; processing said optical signal to a Boolean signal; and defining the start of the assay based on said Boolean signal. The present invention also relates to a method for evaluating the start of an assay comprising an electrical detection of a change in the conductivity or permittivity of fluid due to the dissolving of reagent as mentioned above. Furthermore, the invention relates to a program element or computer program for evaluating the start of an assay and to an evaluation system for determining the start of an assay, comprising a computer processor, memory, and (a) data storage device(s), the memory having programming instructions to execute such a program element or computer program.