diff --git a/addons/l10n_ch/dta/invoice.py b/addons/l10n_ch/dta/invoice.py
index 8af850ef6c2..c228c1b5511 100644
--- a/addons/l10n_ch/dta/invoice.py
+++ b/addons/l10n_ch/dta/invoice.py
@@ -49,11 +49,38 @@ class account_invoice(osv.osv):
 		'dta_state': lambda *a: 'none',
 	}
 
+
+	def _mod10r(self,nbr):
+		"""
+		Input arg : account or invoice number
+		Output return: the same number completed with the recursive mod10
+		key
+		"""
+
+		codec=[0,9,4,6,8,2,7,1,3,5]
+		report = 0
+		result=""
+		for chiffre in nbr:
+			
+			if not chiffre.isdigit():
+				continue
+			
+			report = codec[ (int(chiffre) +report) % 10 ] 
+			result += chiffre
+		return result + str((10-report) % 10)
+
+
+# 0100054150009>132000000000000000000000014+ 1300132412>
 	def _check_bvr(self, cr, uid, ids):
-		return False
+		invoices = self.browse(cr,uid,ids)
+		for invoice in invoices:
+			if invoice.bvr_ref_num and self._mod10r(invoice.bvr_ref_num[:-1]) != invoice.bvr_ref_num:
+				print self._mod10r(invoice.bvr_ref_num[:-1]),"  ",invoice.bvr_ref_num
+				return False
+		return True
 	
 	_constraints = [
-		(_check_bvr, 'Error : Invalid Bvr Number.', [''])
+		(_check_bvr, 'Error : Invalid Bvr Number (wrong checksum).', [''])
 	]