Method for determining the viscosity of substances using a rotational viscometer comprising a measuring shaft driven by a drive, a coupling element, in particular an elastic coupling element, having a maximum angular deflection (φ max) and an optimum angular deflection (φ opt), wherein the optimum angular deflection (φ opt) is smaller than the maximum angular deflection (φ max), wherein the measuring shaft is connected through the coupling element to the drive, and a measuring body which is arranged at one end of the measuring shaft and can be acted upon by a sample, wherein an angle measuring unit is provided which is arranged relative to the measuring shaft and designed in such a way that the angular deflection (φ) between the drive and the measuring shaft can be measured during measuring operation, and wherein the rotational viscometer comprises an evaluation unit to which the angular deflection (φ) of the coupling element measured by the angle measuring unit is fed, wherein the optimum angular deflection (φ opt) of the coupling element is stored in the evaluation unit or is fed thereto before the measurement begins, - wherein in a first step the measuring body is immersed in a measuring container in which the sample is located, - wherein in a second step the rotational speed (n) of the measuring shaft, proceeding from a first measuring point (P 0) at an initial rotational speed (n 0), in particular standstill, is increased stepwise to at least two further measuring points (P 1, P 2) at respective rotational speeds (n 1, n 2) and the respective angular deflection (φ 0, φ 1, φ 2) between the drive and the measuring shaft is determined at the individual measuring points (P 0, P 1, P 2), - wherein in a third step an estimation function (φ = f(n, t)) is determined for the relationship between the rotational speed (n) and the angular deflection (φ) for the sample using the measured values determined at the measuring points (P 0, P 1, P 2), - wherein in a fourth step, on the basis of the estimation function (φ = f(n, t)), an optimum rotational speed (n opt) is determined at which a previously defined optimum angular deflection (φ opt) is present, and - wherein in a fifth step the viscosity of the sample is measured at the optimum rotational speed (n opt). wherein an angle measuring unit is provided which is arranged relative to the measuring shaft and designed in such a way that the angular deflection (φ) between the drive and the measuring shaft can be measured during measuring operation, and wherein the rotational viscometer comprises an evaluation unit to which the angular deflection (φ) of the coupling element measured by the angle measuring unit is fed, wherein the optimum angular deflection (φ opt) of the coupling element is stored in the evaluation unit or is fed thereto before the measurement begins, - wherein in a first step the measuring body is immersed in a measuring container in which the sample is located, - wherein in a second step the rotational speed (n) of the measuring shaft, proceeding from a first measuring point (P 0) at an initial rotational speed (n 0), in particular standstill, is increased stepwise to at least two further measuring points (P 1, P 2) at respective rotational speeds (n 1, n 2) and the respective angular deflection (φ 0, φ 1, φ 2) between the drive and the measuring shaft is determined at the individual measuring points (P 0, P 1, P 2), - wherein in a third step an estimation function (φ = f(n, t)) is determined for the relationship between the rotational speed (n) and the angular deflection (φ) for the sample using the measured values determined at the measuring points (P 0, P 1, P 2), - wherein in a fourth step, on the basis of the estimation function (φ = f(n, t)), an optimum rotational speed (n opt) is determined at which a previously defined optimum angular deflection (φ opt) is present, and - wherein in a fifth step the viscosity of the sample is measured at the optimum rotational speed (n opt). - wherein in a first step the measuring body is immersed in a measuring container in which the sample is located, - wherein in a second step the rotational speed (n) of the measuring shaft, proceeding from a first measuring point (P 0) at an initial rotational speed (n 0), in particular standstill, is increased stepwise to at least two further measuring points (P 1, P 2) at respective rotational speeds (n 1, n 2) and the respective angular deflection (φ 0, φ 1, φ 2) between the drive and the measuring shaft is determined at the individual measuring points (P 0, P 1, P 2), - wherein in a third step an estimation function (φ = f(n, t)) is determined for the relationship between the rotational speed (n) and the angular deflection (φ) for the sample using the measured values determined at the measuring points (P 0, P 1, P 2), - wherein in a fourth step, on the basis of the estimation function (φ = f(n, t)), an optimum rotational speed (n opt) is determined at which a previously defined optimum angular deflection (φ opt) is present, and - wherein in a fifth step the viscosity of the sample is measured at the optimum rotational speed (n opt).