A method of verifying a measurement accuracy of a level gauge system comprising a measurement unit and a propagation device attached to a tank for propagating electromagnetic signals generated by said measurement unit towards a product in the tank, wherein said method comprises the steps of: feeding, to said propagation device, a first electromagnetic transmit signal generated by said measurement unit; receiving, at said measurement unit, a first electromagnetic reflection signal being a reflection of said first electromagnetic transmit signal at a reference reflector arranged in said tank; determining (100, 201) a first measurement value indicative of a time-of-flight of said first electromagnetic reflection signal from said measurement unit to said reference reflector and back to said measurement unit; feeding, after having determined said first measurement value, to a verification arrangement having at least one known electromagnetic signal propagation property, an electromagnetic signal generated by said measurement unit; receiving, at said measurement unit, a response signal from said verification arrangement, said response signal being indicative of said at least one electromagnetic signal propagation property of said verification arrangement; determining a measurement unit verification measurement value based on said response signal; feeding, after having determined said measurement unit verification measurement value, to said propagation device, a second electromagnetic transmit signal generated by said measurement unit; receiving, at said measurement unit, a second electromagnetic reflection signal being a reflection of said second electromagnetic transmit signal at said reference reflector arranged in said tank; determining (102, 305) a second measurement value indicative of a time-of-flight of said second electromagnetic reflection signal from said measurement unit to said reference reflector and back to said measurement unit; and determining (103, 306) a verification result based on an absolute difference between said first measurement value and said second measurement value, and on said measurement unit verification measurement value, wherein said verification result is positive if the absolute difference between said first measurement value and said second measurement value is smaller than a predefined value. feeding, to said propagation device, a first electromagnetic transmit signal generated by said measurement unit; receiving, at said measurement unit, a first electromagnetic reflection signal being a reflection of said first electromagnetic transmit signal at a reference reflector arranged in said tank; determining (100, 201) a first measurement value indicative of a time-of-flight of said first electromagnetic reflection signal from said measurement unit to said reference reflector and back to said measurement unit; feeding, after having determined said first measurement value, to a verification arrangement having at least one known electromagnetic signal propagation property, an electromagnetic signal generated by said measurement unit; receiving, at said measurement unit, a response signal from said verification arrangement, said response signal being indicative of said at least one electromagnetic signal propagation property of said verification arrangement; determining a measurement unit verification measurement value based on said response signal; feeding, after having determined said measurement unit verification measurement value, to said propagation device, a second electromagnetic transmit signal generated by said measurement unit; receiving, at said measurement unit, a second electromagnetic reflection signal being a reflection of said second electromagnetic transmit signal at said reference reflector arranged in said tank; determining (102, 305) a second measurement value indicative of a time-of-flight of said second electromagnetic reflection signal from said measurement unit to said reference reflector and back to said measurement unit; and determining (103, 306) a verification result based on an absolute difference between said first measurement value and said second measurement value, and on said measurement unit verification measurement value, wherein said verification result is positive if the absolute difference between said first measurement value and said second measurement value is smaller than a predefined value.