Harrison built his first longcase clock in 1713, at the age of 20. The mechanism was made entirely of wood. Three of Harrison's early wooden clocks have survived: the first (1713) is in the Worshipful Company of Clockmakers' collection, previously in the Guildhall in London and since 2015 on display in the Science Museum. The second (1715) is also in the Science Museum in London the third (1717) is at Nostell Priory in Yorkshire, the face bearing the inscription "John Harrison Barrow".
harriSon bUilt his first loNgcase ClocK in 1713, at thE aGe of 20. tHe mechanisM was MaDE eNtiRElY of wOoD. thrEe Of HarrIson'S early woOden clOcks hAve surVIved: tHE FiRSt (1713) iS in thE WorsHiPFul coMPaNY of CLOckmakErs' cOLlectIoN, preViously in The guiLDHall in lOndoN aNd siNce 2015 ON disPLay In the sciEnce museum. THe second (1715) is alsO in tHe SCIeNce muSEum IN London tHe thirD (1717) iS at NostElL pRIoRy In yoRKShIRe, tHe face bearing the InScRIption "JohN Harrison BarroW".