The amount of this guarantee will be automatically increased upon the builder's receipt of the second,third,fourth and fifth instalments ,plus interest thereon as provided in the contract,but in any eventually the amount of this guarantee shall not exceed the total sum of dollars plus interest thereon at the rate of six month dollars libor plus 1.5% per annum from the date following the date of the builder's receipt of each instalment to the date of remittance by telegraphic transfer of the refund