learning how to use the history db

balance.clj

(defn balance-history [id]
  (d/q '[:find ?tx ?tx-time ?v
       :in $ ?e ?a
       :where [?e ?a ?v ?tx _]
       [?tx :db/txInstant ?tx-time]]
     (d/history (db/db)) id :account/balance))

@(d/transact conn [[:credit 17592186145525 100]])

(balance-history 17592186145525)
; => #{[13194139534419 #inst "2013-09-20T09:04:56.730-00:00" 0]
;      [13194139534419 #inst "2013-09-20T09:04:56.730-00:00" 100]
;      [13194139534415 #inst "2013-09-20T09:00:49.186-00:00" 0]}
; why does this return three results? I want only two: the first 0 and 100.

schema.edn

[
 {:db/id #db/id[:db.part/db]
  :db/ident :account/balance
  :db/cardinality :db.cardinality/one
  :db/valueType :db.type/bigint
  :db.install/_attribute :db.part/db}

 {:db/id #db/id [:db.part/user]
  :db/ident :credit
  :db/fn #db/fn {:lang "clojure"
                 :params [db id amount]
                 :code [[:db/add id :account/balance (biginteger balance)]]}}
 ]

the answer was to restrict ?added (the fifth field in the query pattern) to true: :where [?e ?a ?v ?tx true]