The asymmetrical double-sided two-way ranging means uneven session duration, as a result clocks errors propagate differently in the two TWR measurement sessions. The article proposes a method of the errors compensation by weighted mean of two TWR measurements and minimization of error expectation. By this method, the offset error is cancelled, the full-scale error is not diminished, the cumulated noise variance is attenuated, and the correlated noises variance is strongly diminished. The error analysis shows that the minimum lower band is reached by SDS-TWR.