diff --git a/modules/purchase_trade/purchase.py b/modules/purchase_trade/purchase.py
index cea3eea..dba26a1 100755
--- a/modules/purchase_trade/purchase.py
+++ b/modules/purchase_trade/purchase.py
@@ -983,7 +983,7 @@ class QualityAnalysis(ModelSQL,ModelView):
 class Line(metaclass=PoolMeta):
     __name__ = 'purchase.line'
 
-    quantity_theorical = fields.Numeric("Th. quantity", digits='unit', readonly=False)
+    quantity_theorical = fields.Numeric("Contractual Qt", digits='unit', readonly=False)
     price_type = fields.Selection([
         ('cash', 'Cash Price'),
         ('priced', 'Priced'),
@@ -1212,6 +1212,16 @@ class Line(metaclass=PoolMeta):
 
     @classmethod
     def write(cls, *args):
+        # Agents:
+        # Ici on gère la variation éventuelle de la théorical quantity après création du contrat
+        # Si delta > 0 on met à jour le lot virtual qui est toujours unique pour une purchase line
+        # mais aussi la table lot_qt dont le lot_p est ce lot virtuel (ajuster lot_quantity)
+        # si il n'existe aucun lot_qt non shippé (tous les lot_shipments à None) et aucun non matché (lot_s à None) 
+        # alors il faut créer un nouveau lot_qt non shippé et non matché avec le delta
+        # Si delta négatif alors on decrease si c'est possible le lot_qt non shippé non matché et s'il n'y en a pas on envoie un 
+        # message d'erreur 'Please unlink or unmatch lot'
+        Lot = Pool().get('lot.lot')
+        LotQt = Pool().get('lot.qt')
         old_values = {}
 
         for records, values in zip(args[::2], args[1::2]):
@@ -1224,11 +1234,57 @@ class Line(metaclass=PoolMeta):
         lines = sum(args[::2], [])
         for line in lines:
             if line.id in old_values:
-                old = old_values[line.id]
-                new = line.quantity_theorical
-                delta = Decimal(new) - Decimal(old)
+                old = Decimal(old_values[line.id] or 0)
+                new = Decimal(line.quantity_theorical or 0)
+                delta = new - old
                 if delta > 0:
-                    continue
+                    virtual_lots = [lot for lot in (line.lots or []) if lot.lot_type == 'virtual']
+                    if not virtual_lots:
+                        continue
+                    vlot = virtual_lots[0]
+                    new_qty = round(Decimal(vlot.get_current_quantity_converted() or 0) + delta, 5)
+                    vlot.set_current_quantity(new_qty, new_qty, 1)
+                    Lot.save([vlot])
+                    lqts = LotQt.search([
+                        ('lot_p', '=', vlot.id),
+                        ('lot_s', '=', None),
+                        ('lot_shipment_in', '=', None),
+                        ('lot_shipment_internal', '=', None),
+                        ('lot_shipment_out', '=', None),
+                    ])
+                    if lqts:
+                        lqt = lqts[0]
+                        lqt.lot_quantity = round(Decimal(lqt.lot_quantity or 0) + delta, 5)
+                        LotQt.save([lqt])
+                    else:
+                        lqt = LotQt()
+                        lqt.lot_p = vlot.id
+                        lqt.lot_s = None
+                        lqt.lot_quantity = round(delta, 5)
+                        lqt.lot_unit = line.unit
+                        LotQt.save([lqt])
+                elif delta < 0:
+                    virtual_lots = [lot for lot in (line.lots or []) if lot.lot_type == 'virtual']
+                    if not virtual_lots:
+                        continue
+                    vlot = virtual_lots[0]
+                    decrease = abs(delta)
+                    lqts = LotQt.search([
+                        ('lot_p', '=', vlot.id),
+                        ('lot_s', '=', None),
+                        ('lot_shipment_in', '=', None),
+                        ('lot_shipment_internal', '=', None),
+                        ('lot_shipment_out', '=', None),
+                    ])
+                    if (not lqts
+                            or Decimal(lqts[0].lot_quantity or 0) < decrease):
+                        raise UserError("Please unlink or unmatch lot")
+                    new_qty = round(Decimal(vlot.get_current_quantity_converted() or 0) - decrease, 5)
+                    vlot.set_current_quantity(new_qty, new_qty, 1)
+                    Lot.save([vlot])
+                    lqt = lqts[0]
+                    lqt.lot_quantity = round(Decimal(lqt.lot_quantity or 0) - decrease, 5)
+                    LotQt.save([lqt])
 
     @classmethod
     def copy(cls, lines, default=None):