diff --git a/modules/purchase_trade/purchase.py b/modules/purchase_trade/purchase.py
index 81a355a..0f16b5d 100755
--- a/modules/purchase_trade/purchase.py
+++ b/modules/purchase_trade/purchase.py
@@ -537,7 +537,7 @@ class AssayImporter:
         pool = Pool()
         self.AssayLine = pool.get('assay.line')
         self.Element = pool.get('assay.element')
-        self.Uom = pool.get('product.uom')
+        self.Unit = pool.get('assay.unit')
 
     # -----------------------------
     # PUBLIC ENTRYPOINT
@@ -599,7 +599,7 @@ class AssayImporter:
         line.assay = assay
         line.element = self._get_or_create_element(item.get('element'))
         line.value = self._safe_float(item.get('value'))
-        line.unit = self._get_uom(item.get('unit'))
+        line.unit = self._get_unit(item.get('unit'))
         line.category = category
 
         line.method = item.get('method')
@@ -624,13 +624,13 @@ class AssayImporter:
         element.save()
         return element
 
-    def _get_uom(self, unit_name):
+    def _get_unit(self, unit_name):
         if not unit_name:
             return None
 
-        uoms = self.Uom.search([('symbol', '=', unit_name)])
-        if uoms:
-            return uoms[0]
+        units = self.Unit.search([('symbol', '=', unit_name)])
+        if units:
+            return units[0]
 
         return None  # ou lever une erreur selon ton besoin
 
@@ -660,7 +660,19 @@ class AssayImporter:
             return 'umpire'
 
         return 'provisional'
-    
+
+class AssayUnit(ModelSQL, ModelView):
+    'Assay Unit'
+    __name__ = 'assay.unit'
+
+    name = fields.Char('Name')         # Percent, g/t, ppm
+    symbol = fields.Char('Symbol')     # %, g/t, ppm
+    dimension = fields.Selection([
+        ('mass_fraction', 'Mass Fraction'),
+        ('grade', 'Grade'),
+        ('trace', 'Trace'),
+    ])
+
 class Assay(ModelSQL, ModelView):
     "Assay"
     __name__ = 'assay.assay'
@@ -701,7 +713,7 @@ class AssayLine(ModelSQL, ModelView):
 
     value = fields.Float("Value")
 
-    unit = fields.Many2One('product.uom', "Unit")
+    unit = fields.Many2One('assay.unit', "Unit")
 
     category = fields.Selection([
         ('assay', 'Assay'),