The Equivalent was a sum negotiated at £398,000 paid to Scotland by the English Government under the terms of the Acts of Union 1707. Proposals for it first emerged in the course of abortive Union negotiations in 1702/03.
The purpose of The Equivalent was ostensibly to take account of the contribution which Scots taxpayers would thereafter make towards servicing the English national debt, and as transitional mitigation of the effects of higher taxes on the Scottish economy. Though attempts have been made to see it as a precise calculation, it is now generally regarded as part of a political bargain designed for other purposes as well, such as the costs of winding up the Company of Scotland which had undertaken the Darien scheme; shareholders in and creditors of the Company were to receive 58.6% of The Equivalent.
For further information on the context and background see Acts of Union 1707.