diff --git a/hwe/func.php b/hwe/func.php
index e7ea5903..0284e298 100644
--- a/hwe/func.php
+++ b/hwe/func.php
@@ -923,6 +923,13 @@ function banner()
 
 function addTurn($date, int $turnterm, int $turn = 1, bool $withFraction = true)
 {
+    if($turnterm < 0){
+        if($turnterm == -60){
+            return VarTurn60::fromDatetime(new \DateTimeImmutable(($date)))->addTurn($turn )->toDateStr($withFraction);
+        }
+        throw new \Exception("InvalidTurnTerm".$turnterm);
+    }
+
     $date = new \DateTime($date);
     $target = $turnterm * $turn;
     $date->add(new \DateInterval("PT{$target}M"));
@@ -934,6 +941,13 @@ function addTurn($date, int $turnterm, int $turn = 1, bool $withFraction = true)
 
 function subTurn($date, int $turnterm, int $turn = 1, bool $withFraction = true)
 {
+    if($turnterm < 0){
+        if($turnterm == -60){
+            return VarTurn60::fromDatetime(new \DateTimeImmutable(($date)))->addTurn($turn * -1)->toDateStr($withFraction);
+        }
+        throw new \Exception("InvalidTurnTerm".$turnterm);
+    }
+
     $date = new \DateTime($date);
     $target = $turnterm * $turn;
     $date->sub(new \DateInterval("PT{$target}M"));
@@ -945,6 +959,14 @@ function subTurn($date, int $turnterm, int $turn = 1, bool $withFraction = true)
 
 function cutTurn($date, int $turnterm, bool $withFraction = true)
 {
+    if($turnterm < 0){
+        if($turnterm == -60){
+            [$baseDate, ] = VarTurn60::fromDatetime(new \DateTimeImmutable(($date)))->cutTurn($withFraction);
+            return $baseDate;
+        }
+        throw new \Exception("InvalidTurnTerm".$turnterm);
+    }
+
     $date = new \DateTime($date);
 
     $baseDate = new \DateTime($date->format('Y-m-d'));
@@ -963,6 +985,8 @@ function cutTurn($date, int $turnterm, bool $withFraction = true)
 
 function cutDay($date, int $turnterm, bool $withFraction = true)
 {
+    assert($turnterm > 0);
+
     $date = new \DateTime($date);
 
     $baseDate = new \DateTime($date->format('Y-m-d'));