diff --git a/estimate_relative_pbh_velocity_from_halo_mass.py b/estimate_relative_pbh_velocity_from_halo_mass.py
new file mode 100644
index 0000000..207b737
--- /dev/null
+++ b/estimate_relative_pbh_velocity_from_halo_mass.py
@@ -0,0 +1,28 @@
+import numpy as np
+
+G = 42.981 #everything here is in Gadget-units
+
+def v_halo_from_mass(m_halo:int, L_box: float, N_res:int, m_particle:float):
+
+    m_box = N_res**3 * m_particle 
+
+    rho_mean = m_box / (L_box ** 3)
+    rho_halo = 200 * rho_mean
+
+    r_halo = (3 * m_halo / (4 * np.pi * rho_halo)) ** (1/3)
+
+    v_halo = np.sqrt(G * m_halo / r_halo)
+
+    return v_halo
+
+v_result = v_halo_from_mass(m_halo=0.000067742, L_box=30.0, N_res=128, m_particle=0.1107263)
+
+print(v_result)
+
+
+# #Results:
+# 11.75 for 0.067742 * 10^10 / h
+# 6.21 for 0.01 ...
+# 2.88 for 0.001 ...
+# 1.17 for 0.000067742 ... (i.e. 10^6 M_sun halos, i.e. three orders of magnitude smaller than the 10^9 we started with)
+
diff --git a/remap_particle_IDs.py b/remap_particle_IDs.py
index 32efed9..963718f 100644
--- a/remap_particle_IDs.py
+++ b/remap_particle_IDs.py
@@ -31,7 +31,7 @@ def downscale_IDs(particle_ID: int, Nres_max: int, Nres_min: int):
 
 
 if __name__ == "__main__":
-    test_particle = np.array([0, 0, 127])
+    test_particle = np.array([1, 1, 0])
     # maximum_test = np.array([127, 127, 127]) #this works, Nres - 1 is the maximum for (i,j,k)
 
     Nres_1 = 128