A fill level measuring device (101, 401, 701) for mounting in a dome-shaft (303, 503), which is arranged in a vertex area of a container (301, 501), and for determining a position of a fill level (d L) of a filling material and/or of a separating layer (d L) between two filling materials in the container (301, 501), wherein the fill level measuring device (101, 401, 701) is configured to emit electromagnetic or acoustical waves towards a filling material surface, the fill level measuring device (101, 401, 701) comprising: an echo-curve acquisition device (102, 110) for capturing at least one echo-curve; an echo-curve identification device for evaluating the at least one echo-curve; a tracking device for grouping echoes from various measurement cycles in a way, that echoes, which are caused by the same reflection spot in the container and that emerge from the same signal paths, are combined to tracks; and a multiple-echo detection device for classifying at least one first echo (515, 610, E MLN1) as a multiple echo of a filling material reflection and of a second echo (515, 611, E MLN2) as a multiple echo; characterized in that the fill level measuring device (101, 401, 701) further has a self-learn device, which is designed for automatically determining a dome-shaft length d D (503, 613) of the dome-shaft (303, 503) by using the first echo (515, 610, E MLN1) classified by the multiple-echo detection device, which has a first electrical distance (D MN1), and the second echo (515, 611, E MLN2), which has a second electrical distance (D MN2), wherein the self-learn device is configured to infer the dome-shaft length d D (503, 613) according to this formula: d D = N 1 + 1 ⋅ D MN 2 − N 2 + 1 ⋅ D MN 1 ε L ⋅ μ L ⋅ N 1 − N 2, wherein N 1 defines the order of the multiple echo at the first electrical distance D MN1, N 2 defines the order of the multiple echo at the second electrical distance D MN2, and ε L describes the relative permittivity and μ L describes the relative permeability of an overlay medium. an echo-curve acquisition device (102, 110) for capturing at least one echo-curve; an echo-curve identification device for evaluating the at least one echo-curve; a tracking device for grouping echoes from various measurement cycles in a way, that echoes, which are caused by the same reflection spot in the container and that emerge from the same signal paths, are combined to tracks; and a multiple-echo detection device for classifying at least one first echo (515, 610, E MLN1) as a multiple echo of a filling material reflection and of a second echo (515, 611, E MLN2) as a multiple echo; characterized in that the fill level measuring device (101, 401, 701) further has a self-learn device, which is designed for automatically determining a dome-shaft length d D (503, 613) of the dome-shaft (303, 503) by using the first echo (515, 610, E MLN1) classified by the multiple-echo detection device, which has a first electrical distance (D MN1), and the second echo (515, 611, E MLN2), which has a second electrical distance (D MN2), wherein the self-learn device is configured to infer the dome-shaft length d D (503, 613) according to this formula: d D = N 1 + 1 ⋅ D MN 2 − N 2 + 1 ⋅ D MN 1 ε L ⋅ μ L ⋅ N 1 − N 2, wherein N 1 defines the order of the multiple echo at the first electrical distance D MN1, N 2 defines the order of the multiple echo at the second electrical distance D MN2, and ε L describes the relative permittivity and μ L describes the relative permeability of an overlay medium.