diff --git a/docs/tutorials/quickstart.ipynb b/docs/tutorials/quickstart.ipynb
index 4067e8c..5bd91ac 100644
--- a/docs/tutorials/quickstart.ipynb
+++ b/docs/tutorials/quickstart.ipynb
@@ -65,7 +65,17 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "pm.pp.split_signal(adata)"
+    "pm.pp.split_signal(adata, var_key=\"channel\")"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "2b1204cf",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "pm.pl.plotdata(adata)"
    ]
   },
   {
diff --git a/pytometry/__init__.py b/pytometry/__init__.py
index 6222248..8dfc6f0 100644
--- a/pytometry/__init__.py
+++ b/pytometry/__init__.py
@@ -26,5 +26,3 @@
 from . import preprocessing as pp
 from . import read_write as io
 from . import tools as tl
-
-# from ._core import ExampleClass, example_function  # noqa
diff --git a/pytometry/_core.py b/pytometry/_core.py
deleted file mode 100644
index f6882ed..0000000
--- a/pytometry/_core.py
+++ /dev/null
@@ -1,26 +0,0 @@
-def example_function(column_name: str) -> str:
-    """Lower case your input string.
-
-    Args:
-        column_name: Column name to transform to lower case.
-
-    Returns:
-        The lower-cased column name.
-    """
-    return column_name.lower()
-
-
-class ExampleClass:
-    """Awesome class."""
-
-    def __init__(self, value: int):
-        print("initializing")
-
-    def bar(self) -> str:
-        """Bar function."""
-        return "hello"
-
-    @property
-    def foo(self) -> str:
-        """Foo property."""
-        return "hello"
diff --git a/pytometry/plotting/_histogram.py b/pytometry/plotting/_histogram.py
index 483d5bf..700eccc 100644
--- a/pytometry/plotting/_histogram.py
+++ b/pytometry/plotting/_histogram.py
@@ -49,7 +49,7 @@ def plotdata(
                 " normalization."
             )
 
-    if option_key not in ["area", "height", "other"]:
+    if option_key.lower() not in ["area", "height", "other"]:
         print(f"Option {option_key} is not a valid category. Return all.")
         datax = adata_.X
         var_names = adata_.var_names.values
@@ -71,10 +71,10 @@ def plotdata(
     number = len(names)
 
     columns = 3
-    rows = np.ceil(number / columns)
+    rows = int(np.ceil(number / columns))
 
     fig = plt.figure()
-    fig.subplots_adjust(hspace=0.4, wspace=0.6)
+    fig.subplots_adjust(hspace=0.8, wspace=0.6)
 
     for idx in range(number):
         ax = fig.add_subplot(rows, columns, idx + 1)