@@ -138,7 +138,7 @@ def _mdtraj_summary(wizard, context, result):
         builder=partial(_mdtraj_cv_builder, func_name='compute_angles'),
         prerequisite=TOPOLOGY_CV_PREREQ,
         intro=_MDTRAJ_INTRO.format(user_str="angle made by three atoms"),
-        description=...,
+        description="This CV will calculate the angle between three atoms.",
         summary=_mdtraj_summary,
     )
 
@@ -148,7 +148,8 @@ def _mdtraj_summary(wizard, context, result):
         builder=partial(_mdtraj_cv_builder, func_name='compute_dihedrals'),
         prerequisite=TOPOLOGY_CV_PREREQ,
         intro=_MDTRAJ_INTRO.format(user_str="dihedral made by four atoms"),
-        description=...,
+        description=("This CV will calculate the dihedral angle made by "
+                     "four atoms"),
         summary=_mdtraj_summary,
     )
 
 
@@ -45,6 +45,37 @@ def force_exit(cmd, ctx):
     'restart': _RESTART_HELP,
 }
 
+
+_SHORT_EVAL_HELP = ("This parameter can be generated using our custom "
+                    "evaluation method. For details, ask for help with "
+                    "'?eval'.")
+_LONG_EVAL_HELP = ("The value for this parameter can be generated using a "
+                   "Python-like syntax. You're limited to a single "
+                   "expression (generally, a single line of Python) and "
+                   "the imports math and numpy (as np). However, this "
+                   "allows you to do simple calculations such as:\n"
+                   "   100 * np.pi / 180  # 100 degrees in radians")
+class EvalHelperFunc:
+    """Helper function (input to :class:`.Helper`) for evaluated parameters.
+
+    Parameters
+    ----------
+    param_helper : str or Callable[str, dict] -> str
+        help string or method that takes arguments and context dict and
+        results the help string
+    """
+    def __init__(self, param_helper, context=None):
+        if isinstance(param_helper, str):
+            helper = lambda wizard, context: param_helper
+        else:
+            helper = param_helper
+        self.helper = helper
+
+    def __call__(self, helpargs, context):
+        if helpargs == "eval":
+            return _LONG_EVAL_HELP
+        return self.helper(helpargs, context) + "\n\n" + _SHORT_EVAL_HELP
+
 class Helper:
     """Manage help and command passing on command line.
 
 
@@ -4,6 +4,7 @@
     LoadFromOPS, WizardParameterObjectPlugin, WizardObjectPlugin,
     WrapCategory
 )
+from paths_cli.wizard.helper import EvalHelperFunc, Helper
 from paths_cli.wizard.plugin_registration import get_category_wizard
 from paths_cli.wizard.core import interpret_req
 import paths_cli.compiling.volumes
@@ -22,6 +23,9 @@ def _binary_func_volume(wizard, context, op):
     vol = op(vol1, vol2)
     return vol
 
+_LAMBDA_HELP = ("This is the {minmax} boundary value for this volume. "
+                "Note that periodic CVs will correctly wrap values "
+                "outside the periodic bounds.")
 _LAMBDA_STR = ("What is the {minmax} allowed value for "
                "'{{obj_dict[cv].name}}' in this volume?")
 CV_DEFINED_VOLUME_PLUGIN = WizardParameterObjectPlugin.from_proxies(
@@ -38,12 +42,16 @@ def _binary_func_volume(wizard, context, op):
         ProxyParameter(
             name="lambda_min",
             ask=_LAMBDA_STR.format(minmax="minimum"),
-            helper="foo",
+            helper=Helper(
+                EvalHelperFunc(_LAMBDA_HELP.format(minmax="minimum"))
+            ),
         ),
         ProxyParameter(
             name='lambda_max',
             ask=_LAMBDA_STR.format(minmax="maximum"),
-            helper="foo",
+            helper=Helper(
+                EvalHelperFunc(_LAMBDA_HELP.format(minmax="maximum"))
+            ),
         ),
     ],
     compiler_plugin=paths_cli.compiling.volumes.CV_VOLUME_PLUGIN,
 
@@ -65,8 +65,13 @@ def _speak(self, content, preface):
         lines = statement.split("\n")
         wrapped = textwrap.wrap(lines[0], width=width, subsequent_indent=" "*3)
         for line in lines[1:]:
-            wrap_line = textwrap.indent(line, " "*3)
-            wrapped.append(wrap_line)
+            if line == "":
+                wrapped.append("")
+            wrap_line = textwrap.wrap(line, width=width,
+                                      initial_indent=" "*3,
+                                      subsequent_indent=" "*3)
+            # wrap_line = textwrap.indent(line, " "*3)
+            wrapped.extend(wrap_line)
         self.console.print("\n".join(wrapped))
 
     @get_object