diff --git a/secop_psi/softcal.py b/secop_psi/softcal.py
index a56c865..bfa06a1 100644
--- a/secop_psi/softcal.py
+++ b/secop_psi/softcal.py
@@ -85,7 +85,7 @@ class Parser340(StdParser):
                         self.logx, self.logy = True, True  # logOhm, logK
                     elif value not in ('1', '2', '3'):
                         raise ValueError('invalid Data Format')
-            elif line.contains('No.'):
+            elif 'No.' in line:
                 self.header = False
             return
         super().parse(line)
@@ -139,16 +139,26 @@ class CalCurve:
         cls, args = KINDS.get(kind, (StdParser, {}))
         args.update(optargs)
 
-        parser = cls(**args)
-        with open(filename) as f:
-            for line in f:
-                parser.parse(line)
+        try:
+            parser = cls(**args)
+            with open(filename) as f:
+                for line in f:
+                    parser.parse(line)
+        except Exception as e:
+            raise ValueError('calib curve %s: %s' % (calibspec, e))
         self.convert_x = nplog if parser.logx else linear
         self.convert_y = npexp if parser.logy else linear
+        x = np.asarray(parser.xdata)
+        y = np.asarray(parser.ydata)
+        if np.all(x[:-1] > x[1:]):  # all decreasing
+            x = np.flip(x)
+            y = np.flip(y)
+        elif np.any(x[:-1] >= x[1:]):  # some not increasing
+            raise ValueError('calib curve %s is not monotonic' % calibspec)
         try:
-            self.spline = splrep(np.asarray(parser.xdata), np.asarray(parser.ydata), s=0)
-        except:
-            raise ValueError('invalid curve, may be not monotonic?')
+            self.spline = splrep(x, y, s=0, k=min(3, len(x) - 1))
+        except (ValueError, TypeError):
+            raise ValueError('invalid calib curve %s' % calibspec)
 
     def __call__(self, value):
         """convert value
@@ -169,9 +179,12 @@ class Sensor(Readable):
     status = Parameter(default=(Readable.Status.ERROR, 'unintialized'))
 
     pollerClass = None
-    description = 'a calibrated sensor value'
     _value_error = None
 
+    def __init__(self, name, logger, cfgdict, srv):
+        cfgdict.setdefault('description', 'calibrated value of module %r' % cfgdict['rawsensor'])
+        super().__init__(name, logger, cfgdict, srv)
+
     def initModule(self):
         self._rawsensor.registerCallbacks(self, ['status'])  # auto update status
         self._calib = CalCurve(self.calib)