The formula (V) is proposed to calculate the ISP time for the double-buffer approach. The formula (V) is derived from (III) with assumption (VI). In (VI) is assumed that buffer programming time is shorter than a flash page programming time (tB), which is given in the datasheet. As it is shown later the assumption (VI) holds in case of most on-chip and on-board flashes unless the flash has extraordinary small page programming time. In addition, formula (VI) bounds the speed of communication with external tester (h) from the lower side, when the equation is satisfied.