diff --git a/examples/dispersion_playground.py b/examples/dispersion_playground.py
new file mode 100644
index 0000000..bcae11b
--- /dev/null
+++ b/examples/dispersion_playground.py
@@ -0,0 +1,98 @@
+import scgenerator as sc
+from plotapp import PlotApp
+import numpy as np
+from PySide6 import QtWidgets
+
+
+def get_disp(w_c, wl, ind, beta):
+    disp = sc.fiber.dispersion_from_coefficients(w_c, list(beta))
+    return sc.units.D_ps_nm_km.inv(sc.fiber.beta2_to_dispersion_parameter(disp[ind], wl * 1e-9))
+
+
+def main():
+    beta2_coefficients = [
+        -1.183e-26,
+        8.1038e-41,
+        -9.5205e-56,
+        2.0737e-70,
+        -5.3943e-85,
+        1.3486e-99,
+        -2.5495e-114,
+        3.0524e-129,
+        -1.714e-144,
+    ]
+    ranges = {}
+    for i, b in enumerate(beta2_coefficients):
+        i += 2
+        ranges[f"beta{i:02}"] = np.linspace(-np.abs(b) * 10, np.abs(b) * 10, 3000)
+
+    wl0 = 1550e-9
+    dt = 1.6e-15
+    t_num = 4096
+    t = sc.math.tspace(t_num=t_num, dt=dt)
+    w_c = sc.math.wspace(t)
+    w = w_c + sc.units.m_rads(wl0)
+    wl = sc.units.m_rads(w)
+
+    wl, ind, _ = sc.PlotRange(500, 3500, "nm").sort_axis(wl)
+    disp0 = get_disp(w_c, wl, ind, beta2_coefficients)
+
+    with PlotApp(**ranges) as app:
+
+        def reset():
+            for i, r in enumerate(app.params.values()):
+                r.value = beta2_coefficients[i]
+
+        def print_beta():
+            keys = sorted(app.params.keys())
+            values = [app.params[k].value for k in keys]
+            print("[\n" + ",\n".join(format(v, "g") for v in values) + "\n]")
+
+        print_beta()
+
+        app[0].set_line_data("original", wl, disp0)
+        app[0].horizontal_line("zero", 0, color="k")
+        app[0].vertical_line("pump", wl0 * 1e9, color="k")
+
+        reset_btn = QtWidgets.QPushButton("Reset")
+        reset_btn.clicked.connect(reset)
+        app.params_layout.addWidget(reset_btn, *divmod(len(app.params), 2))
+        reset()
+
+        print_btn = QtWidgets.QPushButton("Reset")
+        print_btn.clicked.connect(print_beta)
+        app.params_layout.addWidget(print_btn, *divmod(len(app.params) + 1, 2))
+
+        @app.update
+        def draw(
+            beta02,
+            beta03,
+            beta04,
+            beta05,
+            beta06,
+            beta07,
+            beta08,
+            beta09,
+            beta10,
+        ):
+            disp = get_disp(
+                w_c,
+                wl,
+                ind,
+                [
+                    beta02,
+                    beta03,
+                    beta04,
+                    beta05,
+                    beta06,
+                    beta07,
+                    beta08,
+                    beta09,
+                    beta10,
+                ],
+            )
+            app[0].set_line_data("dispersion", wl, disp)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/src/scgenerator/math.py b/src/scgenerator/math.py
index 8af17b5..5a8eb17 100644
--- a/src/scgenerator/math.py
+++ b/src/scgenerator/math.py
@@ -127,10 +127,6 @@ def normalized(z: np.ndarray) -> np.ndarray:
     return ab / ab.max()
 
 
-def sigmoid(x):
-    return 1 / (np.exp(-x) + 1)
-
-
 def to_dB(arr: np.ndarray, ref=None, axis=None, default: float | None = None) -> np.ndarray:
     """
     converts unitless values in dB
diff --git a/src/scgenerator/spectra.py b/src/scgenerator/spectra.py
index f286a7c..ce044db 100644
--- a/src/scgenerator/spectra.py
+++ b/src/scgenerator/spectra.py
@@ -527,7 +527,6 @@ def propagation(
         io = ZipFileIOHandler(file)
     else:
         io = MemoryIOHandler()
-
     try:
         return _create_new_propagation(io, params, bundle_data)
     except Exception as e: