diff --git a/src/sakia/core/money/quant_zerosum.py b/src/sakia/core/money/quant_zerosum.py
index 9bb7e21124a238988bfdbdf17189baf51462231b..703441e6530e5a81eaa0d69a3c6e08b738f8bdf0 100644
--- a/src/sakia/core/money/quant_zerosum.py
+++ b/src/sakia/core/money/quant_zerosum.py
@@ -2,6 +2,7 @@ from PyQt5.QtCore import QCoreApplication, QT_TRANSLATE_NOOP, QLocale
 from . import Quantitative
 import asyncio
 
+
 class QuantitativeZSum:
     _NAME_STR_ = QT_TRANSLATE_NOOP('QuantitativeZSum', 'Quant Z-sum')
     _REF_STR_ = QT_TRANSLATE_NOOP('QuantitativeZSum', "{0} Q0 {1}")
@@ -22,7 +23,7 @@ class QuantitativeZSum:
 
     @classmethod
     def diff_units(cls, currency):
-        return QuantitativeZSum.units(currency)
+        return Quantitative.units(currency)
 
     @asyncio.coroutine
     def value(self):
@@ -63,4 +64,4 @@ class QuantitativeZSum:
     @asyncio.coroutine
     def diff_localized(self, units=False, international_system=False):
         localized = yield from Quantitative(self.amount, self.community, self.app).localized(units, international_system)
-        return localized
\ No newline at end of file
+        return localized
diff --git a/src/sakia/core/money/quantitative.py b/src/sakia/core/money/quantitative.py
index e0072fbfb512c4efa42462a455a06157fd4d9018..c54dd74ee3c2b1d67164a8f2f5bedc6f0c4ac38f 100644
--- a/src/sakia/core/money/quantitative.py
+++ b/src/sakia/core/money/quantitative.py
@@ -1,6 +1,7 @@
 from PyQt5.QtCore import QCoreApplication, QT_TRANSLATE_NOOP, QObject, QLocale
 import asyncio
 
+
 class Quantitative():
     _NAME_STR_ = QT_TRANSLATE_NOOP('Quantitative', 'Units')
     _REF_STR_ = QT_TRANSLATE_NOOP('Quantitative', "{0} {1}{2}")
diff --git a/src/sakia/core/money/relative.py b/src/sakia/core/money/relative.py
index 30d83ff4de45c20aa3a0bba11bbdefdd13127bb7..eae0781f81db21f527e2f9881108e3b3d226203c 100644
--- a/src/sakia/core/money/relative.py
+++ b/src/sakia/core/money/relative.py
@@ -1,7 +1,8 @@
 from PyQt5.QtCore import QObject, QCoreApplication, QT_TRANSLATE_NOOP, QLocale
 import asyncio
 
-class Relative():
+
+class Relative:
     _NAME_STR_ = QT_TRANSLATE_NOOP('Relative', 'UD')
     _REF_STR_ = QT_TRANSLATE_NOOP('Relative',  "{0} {1}UD {2}")
     _UNITS_STR_ = QT_TRANSLATE_NOOP('Relative',  "UD {0}")
diff --git a/src/sakia/core/money/relative_zerosum.py b/src/sakia/core/money/relative_zerosum.py
index f32b5274eb0b1c25c36cb46a15166615da4b9b4d..79d3a9f64ac95e6126929ba9c2769ccf341e919b 100644
--- a/src/sakia/core/money/relative_zerosum.py
+++ b/src/sakia/core/money/relative_zerosum.py
@@ -22,7 +22,7 @@ class RelativeZSum:
 
     @classmethod
     def diff_units(cls, currency):
-        return RelativeZSum.units(currency)
+        return Relative.units(currency)
 
     @asyncio.coroutine
     def value(self):