diff --git a/refellips/dispersion.py b/refellips/dispersion.py
index aeccc77..15e4970 100644
--- a/refellips/dispersion.py
+++ b/refellips/dispersion.py
@@ -293,12 +293,12 @@ def complex(self, wavelength):
             wav = wavelength
 
         # Convert between μm & nm (constants are typically given in μm)
-        wav *= 1e-3
+        wav_um = wav * 1e-3
 
         real = np.sqrt(
             self.Einf.value
-            + (self.Am.value * wav**2) / (wav**2 - self.En.value**2)
-            - (self.P.value * wav**2)
+            + (self.Am.value * wav_um**2) / (wav_um**2 - self.En.value**2)
+            - (self.P.value * wav_um**2)
         )
         return real + 1j * 0.0
 
@@ -311,12 +311,12 @@ def epsilon(self, wavelength):
             wav = wavelength
 
         # Convert between μm & nm (constants are typically given in μm)
-        wav *= 1e-3
+        wav_um = wav * 1e-3
 
         real = (
             self.Einf.value
-            + (self.Am.value * wav**2) / (wav**2 - self.En.value**2)
-            - (self.P.value * wav**2)
+            + (self.Am.value * wav_um**2) / (wav_um**2 - self.En.value**2)
+            - (self.P.value * wav_um**2)
         )
 
         return real + 1j * 0
diff --git a/tools/plottools.py b/tools/plottools.py
index fb0387e..23f8e5d 100644
--- a/tools/plottools.py
+++ b/tools/plottools.py
@@ -12,6 +12,7 @@ def plot_ellipsdata(
     xaxis="aoi",
     plot_labels=True,
     legend=True,
+    resax=None,
 ):
     """
     Plots delta and psi values as a function of wavelength or angle of incidence.
@@ -33,31 +34,35 @@ def plot_ellipsdata(
         The default is None.
     objective : refellips.objectiveSE.ObjectiveSE, optional
         Objective (containing model and data) to plot. If the objective is provided,
-        neither model or data should be provided. The default is None.
+        neither model nor data should be provided. The default is None.
     xaxis : String, optional
         Either 'aoi' or 'wavelength'. The default is 'aoi'.
     plot_labels : Bool, optional
         Whether to plot axis labels. The default is True.
     legend : Bool, optional
         Whether to plot the legend. The default is True.
-
+    resax : matplotlib.axes._subplots.AxesSubplot, optional
+        Axis object on which delta and psi residuals. If not provided,
+        no residual will be plotted.
     Returns
     -------
     None.
 
     """
 
-    if objective != None:
+    if objective is not None:
         assert (
-            data == None and model == None
+            data is None and model is None
         ), "If objective is supplied, model and data should not be passed"
         data = objective.data
         model = objective.model
-    elif model != None:
-        assert data != None, "If you supply a model, you must also supply data"
+    elif model is not None:
+        assert (
+            data is not None
+        ), "If you supply a model, you must also supply data"
     else:
         assert (
-            data != None
+            data is not None
         ), "must supply at least one of data, model or objective"
 
     assert (
@@ -72,40 +77,70 @@ def plot_ellipsdata(
         x = data.aoi
         xlab = "AOI (°)"
 
-        if model != None:
+        if model is not None:
             for wav in unique_wavs:
                 psis, deltas = model(np.c_[np.ones_like(aois) * wav, aois])
                 ax.plot(aois, psis, color="r")
                 axt.plot(aois, deltas, color="b")
 
     elif xaxis == "wavelength":
-        unique_aois = np.unique(data.aoi)
+        # Doesn't work for VASE
         wavs = np.linspace(
             np.min(data.wavelength) - 50, np.max(data.wavelength) + 50
         )
         x = data.wavelength
+        xlab = "Wavelength (nm)"
 
-        if model != None:
-            print(x)
-            for idx, wav in enumerate(np.unique(data.wavelength)):
-                wavelength, aoi, d_psi, d_delta = list(
-                    data.unique_wavelength_data()
-                )[idx]
+        if model is not None:
+            wavelength_aois = np.c_[wavs, data.aoi[0] * np.ones_like(wavs)]
+            psi, delta = model(wavelength_aois)
+            ax.plot(wavs, psi, color="r")
+            axt.plot(wavs, delta, color="b")
+    #             for idx, wav in enumerate(np.unique(data.wavelength)):
+    #                 wavelength, aoi, d_psi, d_delta = list(
+    #                     data.unique_wavelength_data()
+    #                 )[idx]
 
-                psi, delta = model(np.c_[np.ones_like(aoi) * wavelength, aoi])
-                ax.plot(np.ones_like(psi) * wavelength, psi, color="r")
-                axt.plot(np.ones_like(delta) * wavelength, delta, color="b")
+    #                 psi, delta = model(np.c_[np.ones_like(aoi) * wavelength, aoi])
+    #                 ax.plot(np.ones_like(psi) * wavelength, psi, color="r")
+    #                 axt.plot(np.ones_like(delta) * wavelength, delta, color="b")
 
-        xlab = "Wavelength (nm)"
+    else:
+        assert False, "xaxis must be 'aoi' or 'wavelength'"
 
-    p = ax.scatter(x, data.psi, color="r")
-    d = axt.scatter(x, data.delta, color="b")
+    # Plot data
+    p = ax.scatter(x, data.psi, color="r", alpha=0.5)
+    d = axt.scatter(x, data.delta, color="b", alpha=0.5)
 
-    ax.legend(handles=[p, d], labels=["Psi", "Delta"])
+    if legend:
+        ax.legend(handles=[p, d], labels=["Psi", "Delta"], loc="center right")
+
+    if resax is not None:
+        assert (
+            objective is not None
+        ), "To plot residuals you must supply an objective"
+        res = objective.residuals()
+        numdp = int(len(res) / 2)
+        psires = res[:numdp]
+        delres = res[numdp:]
+        resax.scatter(x, psires, color="r")
+        resax.scatter(x, delres, color="b")
+        resax.text(
+            0.95,
+            0.1,
+            s=r"$\chi^2 = $" + f"{np.round(objective.chisqr(),3)}",
+            transform=resax.transAxes,
+            ha="right",
+            va="bottom",
+        )
 
     if plot_labels:
-        ax.set(ylabel="Psi", xlabel=xlab)
-        axt.set(ylabel="Delta")
+        ax.set_ylabel("Psi", color="red")
+        ax.set_xlabel(xlab)
+
+        axt.set_ylabel("Delta", color="blue")
+        if resax is not None:
+            resax.set(ylabel="error")
 
 
 def plot_structure(
@@ -131,7 +166,7 @@ def plot_structure(
     objective : refellips.objectiveSE.ObjectiveSE, optional
         Objective (containing model and data) to plot. If the objective is provided,
         structure should not be provided. The default is None.
-    structure : refnx.reflect.structure.Structure
+    structure : refnx.reflect.structure.Structure.
         Structure (which represents the interface) to be plotted. If structure is provided,
         objective should not be provided. The default is None.
     reverse_structure : bool
@@ -144,19 +179,23 @@ def plot_structure(
     None.
 
     """
-    if objective != None:
+    if objective is not None:
         assert (
-            structure == None
+            structure is None
         ), "you must supply either an objective or structure, not both"
         structure = objective.model.structure
         wavelengths = np.unique(objective.data.wavelength)
     else:
         assert (
-            structure != None
+            structure is not None
         ), "you must supply either an objective or structure"
         wavelengths = [658]
 
     if len(wavelengths) > 1:
+        if len(wavelengths) > 8:
+            wavelengths = np.linspace(
+                np.min(wavelengths), np.max(wavelengths), 6
+            )
         colors = plt.cm.viridis(np.linspace(0, 1, len(wavelengths)))
         alpha = 0.5
     else: