Cole, Ch. J.
l. contract: ages. ‘ I. The first proposition relied upon by counsel for appellants is, that the damages resulting to plaintiffs, if any, by reason of the breach of the covenant of the Dubuque and Pacific Bailroad Company to construct and operate the side track, cannot be embraced in the “ indebtedness for the construction of the second forty miles of road ” which the defendant was, by its contract and by the decree, bound to pay.
*544The Dubuque and Pacific Railroad Company was indebted to plaintiffs for “ borrowed land,” used in the construction of its second forty miles of road. This is conceded. That indebtedness it is claimed by appellant’s counsel was paid by the execution and delivery of the covenant, which, under our statute, Revision section 1823, is the same as an unsealed instrument. Rut the making of the covenant did not pay the indebtedness ; that would only be satisfied or paid by the keeping and performing of the obligations of that covenant. So far as the covenant was kept, it operated as payment pro tanto. Whatever of the covenant was not performed left so much of the indebtedness unsatisfied. If the former company had given its covenant to pay an annuity, such covenant, having only the same effect as an unsealed instrument, would have discharged the indebtedness only so far as performed; that portion unperformed would still have remained as an indebtedness; so of the covenant to maintain the side track.
2. . measure of damages, II. The court admitted evidence to prove the difference in annual rental value of the plaintiff’s lots with the side track operated, and without it; and also instructed the jury that the measure of the plaintiffs’ damages, if they found for them, was the aggregated difference in the annual rental values. These are assigned as error.
In our opinion the correct measure of damages is the difference in the value of the plaintiffs’ lots, with the side track operated, and without it, at the time the track was abandoned, together with interest thereon up to date of trial, or not, at the discretion of the jury. This rule renders the ascertainment of the damages easy, certain and final, and limits them to what would surely be within the contemplation of the parties. Whereas, the annual rental value is more speculative and uncertain; is liable *545to great fluctuations from causes not within the scope of the contemplation of the parties, nor indeed within the range of their anticipations; besides, if the damages are apportionable, the measure of difference in annual rent would result in a multiplicity of suits; or, if not apportionable, then the result must be purely speculative (as to future rents), or the plaintiff be barred, by one recovery, from any other. For this error the judgment must be
[Reversed.