diff --git a/src/kyupy/sim.py b/src/kyupy/sim.py
index ef1b2e5..4d4aa3f 100644
--- a/src/kyupy/sim.py
+++ b/src/kyupy/sim.py
@@ -169,7 +169,7 @@ class SimOps:
         self.tmp_idx = self.zero_idx + 1
         self.ppi_offset = self.tmp_idx + 1
         self.ppo_offset = self.ppi_offset + len(self.s_nodes)
-        self.vat_length = self.ppo_offset + len(self.s_nodes)
+        self.vat_len = self.ppo_offset + len(self.s_nodes)
 
         # translate circuit structure into self.ops
         ops = []
@@ -217,7 +217,7 @@ class SimOps:
         self.ops = np.asarray(ops, dtype='int32')
 
         # create a map from fanout lines to stem lines for fork stripping
-        stems = np.zeros(self.vat_length, dtype='int32') - 1  # default to -1: 'no fanout line'
+        stems = np.zeros(self.vat_len, dtype='int32') - 1  # default to -1: 'no fanout line'
         if strip_forks:
             for f in circuit.forks.values():
                 prev_line = f.ins[0]
@@ -228,8 +228,8 @@ class SimOps:
                     stems[ol] = stem_idx
 
         # calculate level (distance from PI/PPI) and reference count for each line
-        levels = np.zeros(self.vat_length, dtype='int32')
-        ref_count = np.zeros(self.vat_length, dtype='int32')
+        levels = np.zeros(self.vat_len, dtype='int32')
+        ref_count = np.zeros(self.vat_len, dtype='int32')
         level_starts = [0]
         current_level = 1
         for i, op in enumerate(self.ops):
@@ -250,7 +250,7 @@ class SimOps:
         self.level_stops = np.asarray(level_starts[1:] + [len(self.ops)], dtype='int32')
 
         # state allocation table. maps line and interface indices to self.state memory locations
-        self.vat = np.zeros((self.vat_length, 3), dtype='int')
+        self.vat = np.zeros((self.vat_len, 3), dtype='int')
         self.vat[:, 0] = -1
 
         h = Heap()
diff --git a/src/kyupy/wave_sim.py b/src/kyupy/wave_sim.py
index 7605b6c..a941eac 100644
--- a/src/kyupy/wave_sim.py
+++ b/src/kyupy/wave_sim.py
@@ -56,7 +56,7 @@ class WaveSim(SimOps):
         self.c_len *= 4
         self.vat[...,0:2] *= 4
 
-        self.timing = np.zeros((self.c_len, 2, 2))
+        self.timing = np.zeros((self.vat_len, 2, 2))
         self.timing[:len(timing)] = timing
 
         self.c = np.zeros((self.c_len, sims), dtype=np.float32) + TMAX