A method of performing spectroscopy in a Transmission Charged-Particle Microscope comprising: - A specimen holder, for holding a specimen; - A source, for producing a beam of charged particles; - An illuminator, for directing said beam so as to irradiate the specimen; - An imaging system, for directing a flux of charged particles transmitted through the specimen onto a spectroscopic apparatus comprising a dispersing device for dispersing said flux into an energy-resolved array of spectral sub-beams, which method comprises the following steps: - Using an adjustable aperture device to admit a first portion of said array to a detector, while blocking a second portion (5b1, 5b2) of said array; - Providing a radiation sensor in said flux upstream of said aperture device; - Using said sensor to perform localized radiation sensing in a selected region of said second portion (5b1, 5b2) of the array, simultaneous with detection of said first portion by said detector, characterized by using a sensing result from said sensor and a detection result from said detector to perform at least one of the following actions: - Deconvolving said detection result using said sensing result and said detection result as input to a mathematical deconvolution procedure; - Correcting for a contribution of an instrument-related transfer function in said detection result; - Determining an absolute energy scale for said detection result; - Determining an absolute intensity scale for said detection result; - Using said sensing result as input to a feedback loop to adjust an output of a power supply connected to at least one of said source, illuminator, imaging system and dispersing device; - Comparing an integrated intensity of the detection result to an integrated intensity of the sensor result so as to derive a thickness value for the specimen. - A specimen holder, for holding a specimen; - A source, for producing a beam of charged particles; - An illuminator, for directing said beam so as to irradiate the specimen; - An imaging system, for directing a flux of charged particles transmitted through the specimen onto a spectroscopic apparatus comprising a dispersing device for dispersing said flux into an energy-resolved array of spectral sub-beams, - Using an adjustable aperture device to admit a first portion of said array to a detector, while blocking a second portion (5b1, 5b2) of said array; - Providing a radiation sensor in said flux upstream of said aperture device; - Using said sensor to perform localized radiation sensing in a selected region of said second portion (5b1, 5b2) of the array, simultaneous with detection of said first portion by said detector, - Deconvolving said detection result using said sensing result and said detection result as input to a mathematical deconvolution procedure; - Correcting for a contribution of an instrument-related transfer function in said detection result; - Determining an absolute energy scale for said detection result; - Determining an absolute intensity scale for said detection result; - Using said sensing result as input to a feedback loop to adjust an output of a power supply connected to at least one of said source, illuminator, imaging system and dispersing device; - Comparing an integrated intensity of the detection result to an integrated intensity of the sensor result so as to derive a thickness value for the specimen.