Add a few minor notes to docs on suffix/siPrefix

pyqtgraph/functions.py

@@ -139,7 +139,8 @@ def siParse(s, regex=FLOAT_REGEX, suffix=None):
         Suffix to check for in ``s``. The default (None) indicates there may or
         may not be a suffix contained in the string and it is returned if
         found. An empty string ``""`` is handled differently: if the string
-        contains a suffix, it is discarded.
+        contains a suffix, it is discarded. This enables interpreting
+        characters following the numerical value as an SI prefix.
     """
     s = asUnicode(s)
     s = s.strip()

pyqtgraph/widgets/SpinBox.py

@@ -132,8 +132,10 @@ class SpinBox(QtGui.QAbstractSpinBox):
         siPrefix       (bool) If True, then an SI prefix is automatically prepended
                        to the units and the value is scaled accordingly. For example,
                        if value=0.003 and suffix='V', then the SpinBox will display
-                       "300 mV" (but a call to SpinBox.value will still return 0.003). Default
-                       is False.
+                       "300 mV" (but a call to SpinBox.value will still return 0.003). In case
+                       the value represents a dimensionless quantity that might span many
+                       orders of magnitude, such as a Reynold's number, an SI
+                       prefix is allowed with no suffix. Default is False.
         step           (float) The size of a single step. This is used when clicking the up/
                        down arrows, when rolling the mouse wheel, or when pressing 
                        keyboard arrows while the widget has keyboard focus. Note that