diff --git a/src/axiomatic/pic_helpers.py b/src/axiomatic/pic_helpers.py
index 3f74acd..b72ba55 100644
--- a/src/axiomatic/pic_helpers.py
+++ b/src/axiomatic/pic_helpers.py
@@ -452,7 +452,7 @@ def print_statements(
                 print("\n-----------------------------------\n")
 
 
-def _str_units_to_float(str_units: str) -> float:
+def _str_units_to_float(str_units: str) -> Optional[float]:
     unit_conversions = {
         "nm": 1e-3,
         "um": 1,
@@ -460,9 +460,9 @@ def _str_units_to_float(str_units: str) -> float:
         "m": 1e6,
     }
     match = re.match(r"([\d\.]+)\s*([a-zA-Z]+)", str_units)
-    numeric_value = float(match.group(1) if match else 1.55)
-    unit = match.group(2) if match else "um"
-    return float(numeric_value * unit_conversions[unit])
+    numeric_value = float(match.group(1)) if match else None
+    unit = match.group(2) if match else None
+    return float(numeric_value * unit_conversions[unit]) if unit in unit_conversions and numeric_value is not None else None
 
 
 def get_wavelengths_to_plot(statements: StatementDictionary, num_samples: int = 100) -> Tuple[List[float], List[float]]:
@@ -484,7 +484,7 @@ def update_wavelengths(mapping: Dict[str, Optional[Computation]], min_wl: float,
                 vlines = vlines | {
                     _str_units_to_float(wl)
                     for wl in (comp.arguments["wavelengths"] if isinstance(comp.arguments["wavelengths"], list) else [])
-                    if isinstance(wl, str)
+                    if isinstance(wl, str) and _str_units_to_float(wl) is not None
                 }
             if "wavelength_range" in comp.arguments:
                 if (
@@ -492,8 +492,11 @@ def update_wavelengths(mapping: Dict[str, Optional[Computation]], min_wl: float,
                     and len(comp.arguments["wavelength_range"]) == 2
                     and all(isinstance(wl, str) for wl in comp.arguments["wavelength_range"])
                 ):
-                    min_wl = min(min_wl, _str_units_to_float(comp.arguments["wavelength_range"][0]))
-                    max_wl = max(max_wl, _str_units_to_float(comp.arguments["wavelength_range"][1]))
+                    mi = _str_units_to_float(comp.arguments["wavelength_range"][0])
+                    ma = _str_units_to_float(comp.arguments["wavelength_range"][1])
+                    if mi is not None and ma is not None:
+                        min_wl = min(min_wl, mi)
+                        max_wl = max(max_wl, ma)
         return min_wl, max_wl, vlines
 
     for cost_stmt in statements.cost_functions or []:
@@ -508,8 +511,8 @@ def update_wavelengths(mapping: Dict[str, Optional[Computation]], min_wl: float,
         min_wl = min(min_wl, min(vlines))
         max_wl = max(max_wl, max(vlines))
     if min_wl >= max_wl:
-        avg_wl = sum(vlines) / len(vlines) if vlines else 1550
-        min_wl, max_wl = avg_wl - 10, avg_wl + 10
+        avg_wl = sum(vlines) / len(vlines) if vlines else 1.55
+        min_wl, max_wl = avg_wl - 0.01, avg_wl + 0.01
     else:
         range_size = max_wl - min_wl
         min_wl -= 0.2 * range_size