diff --git a/src/utils/calUnitTools.js b/src/utils/calUnitTools.js
index 76e348d..a5f6ecb 100644
--- a/src/utils/calUnitTools.js
+++ b/src/utils/calUnitTools.js
@@ -45,6 +45,13 @@ export function subTj(valueArr, unitArr) {
     mixIndex = thisIndex < mixIndex ? thisIndex : mixIndex
   }
 
+  if (mixIndex === -1) {
+    return {
+      total: 0,
+      unit: 'mL'
+    }
+  }
+
   let total = multiplyDecimals(
     parseFloat(valueArr[0]),
     Math.pow(1000, unit.indexOf(unitArr[0]) - mixIndex)