typo, small edits

Author: Bob Grabar

source/core/sharded-clusters.txt

@@ -92,7 +92,7 @@ Shard Balancing
 ---------------
 
 Balancing is the process MongoDB uses to redistribute data within a
-:term:`sharded cluster`. When a :term:`shard` has a too many
+:term:`sharded cluster`. When a :term:`shard` has too many
 :term:`chunks <chunk>` when compared to other shards, MongoDB
 automatically balances the shards. MongoDB balances the shards without
 intervention from the application layer.
@@ -102,9 +102,9 @@ have on the cluster, by:
 
 - Moving only one chunk at a time.
 
-- Only initiating a balancing round when the difference in number of
-  chunks between the shard with the greatest and the shard with the
-  least number of chunks exceeds the :ref:`migration threshold
+- Initiating a balancing round **only** when the difference in the number of
+  chunks between the shard with the greatest number and the shard with the
+  lowest exceeds the :ref:`migration threshold
   <sharding-migration-thresholds>`.
 
 You may disable the balancer on a temporary basis for