Abstract: The present invention is with respect to a reflectance measuring head that is designed for stopping the production of false readings by regular (as opposed to diffuse) reflection and shiny parts of the sample without using normal shine traps or diaphragms. False readings as produced by regular reflection, by surface grain or structure and by inhomogeneity of the surface of the sample are furthermore put an end to by having a number of transmitters placed at an equal distance from one receiver or having a number of receivers placed at an equal distance from a transmitter. A more specially useful effect is produced if a number of transmitters and a number of receivers are placed alternately in the form of a matrix.

Abstract: To be certain of an even illumination of a field of measurement for measuring reflectance and to make it possible to have reflectance measuring heads of small size, the said field is illuminated with a number of discrete beams coming from transmitters, whose emission faces or areas are placed in a plane that is parallel to the plane of the said field. Preferably light guide cables are used for the transmitters and receivers.

Abstract: In known apparatus for taking reflectance readings the accuracy is very highly dependent on the distance between the transmitter and/or receiver area, on the one hand, from the surface whose reflectance is to be measured on the other. In the invention, in the field of measurement, the beam from a transmitter has superimposed on it the beam of at least one further transmitter so that within a wide range of operation readings are made independent of the distance between the said field on the one hand and the transmitter and/or receiver plane on the other and for this reason there is a deep range of measurement, that is to say compensation of depth. Preferably the transmitters are placed axially symmetrically with respect to the axis of the received beam (beam coming from the sample) or planarly symmetrical with respect to a plane containing the axis of the said beam.

Abstract: The invention provides a photometric method of determining courses of reaction in a specimen, in which method the intensities of the transmitted light and of the stray light are measured, wherein the two intensities are measured simultaneously and the electrical signals corresponding to the transmitted light and to the stray light are combined to form one signal. The invention makes it possible to perform reliable measurement even with low levels of transmitted and stray light.The method is preferably used in determining the coagulation times of blood. Apparatus for carrying out the method is also disclosed.