The Psalms of Scottish Metrical Psalter
The Scottish Psalter of 1650 was produced by the Westminster Assembly following careful revision of the version as translated by Francis Rous. This psalter received the sanction of the civil power in 1650 as well as that of the church and is faithful to the orignal text. The psalter is used in the public and private exercises of the Worship of God.
Only the Psalms of David are sung in worship. Professor R. George explains this in the article Why the Psalms only?
No instrumental accompaniment is used in the singing in worship according to the Regulative Principle of Worship. This is explained by Rev. Keith Watkins in the article Musical Instruments in Worship.