diff --git a/benchmarks/sandbox.py b/benchmarks/sandbox.py
index 0a9a04e48..9fd576950 100644
--- a/benchmarks/sandbox.py
+++ b/benchmarks/sandbox.py
@@ -44,20 +44,20 @@ class Sandbox(Runner):
     sandbox = True
 
     # select here the external program between LHA, LHAPDF, apfel, pegasus
-    external = "apfel"
+    external = "void"
     # external = "pegasus"
 
     # select to plot operators
-    plot_operator = True
+    # plot_operator = True
 
-    rotate_to_evolution_basis = True
+    # rotate_to_evolution_basis = True
 
     @staticmethod
     def generate_operators():
         ops = {
             "ev_op_iterations": [1],
             # "ev_op_max_order": [20],
-            "mugrid": [[10]],
+            "mugrid": [[10.0]],
             # "debug_skip_singlet": [True],
         }
         return ops
@@ -118,12 +118,12 @@ def lha(self):
             "FNS": "FFNS",
             "NfFF": 4,
             "ModEv": "EXA",
-            "XIF": np.sqrt(2),
-            "Q0": np.sqrt(2),
+            "XIF": float(np.sqrt(2)),
+            "Q0": float(np.sqrt(2)),
             "kcThr": 0.0,
             "kbThr": np.inf,
             "ktThr": np.inf,
-            "Qref": np.sqrt(2.0),
+            "Qref": float(np.sqrt(2.0)),
             "alphas": 0.35,
         }
         self.skip_pdfs = lambda _theory: [
@@ -139,11 +139,11 @@ def lha(self):
         ]
         self.run(
             [theory_updates],
-            [{"mugrid": [100], "debug_skip_singlet": True}],
+            [{"mugrid": [100.0], "debug_skip_singlet": True}],
             ["ToyLH"],
         )
 
 
 if __name__ == "__main__":
     sand = Sandbox()
-    sand.doit()
+    sand.lha()
diff --git a/src/ekomark/benchmark/runner.py b/src/ekomark/benchmark/runner.py
index e2ea83091..6a75f1437 100644
--- a/src/ekomark/benchmark/runner.py
+++ b/src/ekomark/benchmark/runner.py
@@ -147,6 +147,21 @@ def run_external(self, theory, ocard, pdf):
                 DGLAP result
         """
         # pylint:disable=import-error,import-outside-toplevel
+        if self.external.lower() == "void":
+            xgrid = ocard["interpolation_xgrid"]
+            mugrid = ocard["mugrid"]
+            labels = (
+                br.evol_basis
+                if self.rotate_to_evolution_basis
+                else br.flavor_basis_pids
+            )
+            void = {
+                "target_xgrid": xgrid,
+                "values": {
+                    mu**2: {pid: [0.0] * len(xgrid) for pid in labels} for mu in mugrid
+                },
+            }
+            return void
         if self.external.lower() == "lha":
             from .external import LHA_utils