diff --git a/doublethink/services.py b/doublethink/services.py
index e646998..9402519 100644
--- a/doublethink/services.py
+++ b/doublethink/services.py
@@ -31,24 +31,24 @@ class ServiceRegistry(object):
     by calling `heartbeat(status_info)` periodically.
 
     `status_info` is a dict and must have at least the fields 'role', 'load',
-    and 'ttl'. Certain other fields are populated automatically
-    as in the example below. In addition, services may set arbitrary other
-    fields.
+    and 'ttl'. Certain other fields are populated automatically as in the
+    example below. In addition, services may set arbitrary other fields.
 
     Some information about required fields:
 
        'role': The role of the service. `healthy_service()` and
            `healthy_services()` look up services using this field.
-       'ttl': Specifies the expected time between heartbeats. If a service's 
-           last heartbeat was more than `ttl` seconds ago, it is considered 
-           to be "down". `healthy_services()` and `healthy_service()` never 
-           return entries for services that are considered "down".
+       'ttl': If a service's last heartbeat was more than 'ttl' seconds ago, it
+           is considered to be "down". `healthy_services()` and
+           `healthy_service()` never return entries for services that are
+           considered "down". A sensible convention is to heartbeat 3 times per
+           'ttl', that is, every `ttl/3` seconds.
        'load': An arbitrary numeric value. It is up to each service to populate
            this field in a way that makes sense to the particular service.
            `healthy_service(role)` returns the service with the lowest load
            for the supplied role. Thus load values need to be comparable to
            within the context of a single service, but comparing loads of
-           services of different roles does not necessarily make any sense.
+           services of different roles might not make any sense.
 
     About the 'id' field:
 
@@ -72,7 +72,7 @@ class ServiceRegistry(object):
             'id': 'd0bed0be-d000-d000-f00d-abeefface0ff'     # generated by rethinkdb if not supplied
             'role': 'brozzler-worker',
             'load': 0.5, # load score
-            'ttl': 20.0,
+            'ttl': 60.0,
             'host': 'wbgrp-svc999.us.archive.org',           # set in svcreg.heartbeat() as a fallback
             'pid': 1234,                                     # set in svcreg.heartbeat() as a fallback
             'first_heartbeat': '2015-10-30T03:39:40.080814', # set in svcreg.heartbeat()
@@ -121,9 +121,8 @@ class ServiceRegistry(object):
             service
 
         `status_info` must have at least the fields 'role', 'load', and
-        'ttl'. Some additional fields are populated
-        automatically by this method. If the field 'id' is absent, it will be
-        generated by rethinkdb.
+        'ttl'. Some additional fields are populated automatically by this
+        method. If the field 'id' is absent, it will be generated by rethinkdb.
 
         See the ServiceRegistry class-level documentation for more information
         about the various fields.
@@ -134,8 +133,7 @@ class ServiceRegistry(object):
 
         Raises:
             Exception: if `status_info` is missing a required field, or a
-                `status_info['ttl']` is not a number greater
-                than zero
+                `status_info['ttl']` is not a number greater than zero
         '''
         for field in 'role', 'ttl', 'load':
             if not field in status_info:
@@ -226,12 +224,10 @@ class ServiceRegistry(object):
             candidate['id'] = role
 
             if not 'ttl' in candidate:
-                raise Exception(
-                        "candidate is missing required field "
-                        "'ttl'")
+                raise Exception("candidate is missing required field 'ttl'")
             val = candidate['ttl']
             if not (isinstance(val, float) or isinstance(val, int)) or val <= 0:
-                raise Exception('"ttl" must be a number > 0')
+                raise Exception("'ttl' must be a number > 0")
 
             candidate['first_heartbeat'] = now
             candidate['last_heartbeat'] = now
@@ -268,8 +264,8 @@ class ServiceRegistry(object):
         '''
         Find least loaded healthy service in the registry.
 
-        A service is considered healthy if its 'last_heartbeat' is in the last
-        `ttl` seconds.
+        A service is considered healthy if its 'last_heartbeat' was less than
+        'ttl' seconds ago
 
         Args:
             role (str): role name
@@ -290,8 +286,8 @@ class ServiceRegistry(object):
         '''
         Look up healthy services in the registry.
 
-        A service is considered healthy if its `last_heartbeat` is in the last
-        `ttl` seconds.
+        A service is considered healthy if its 'last_heartbeat' was less than
+        'ttl' seconds ago
 
         Args:
             role (str, optional): role name