The time delay was measured with a picoseconds resolution. However, due to extra systematic errors, such as diffraction contribution, etc., the resulting relative standard uncertainty ΔUtd/Utd for the TOF delay td was estimated as: ΔUtd/Utd=±0.1%. Similarly, the relative standard uncertainty of the path L (resulting from calibration measurements in water) was estimated as: ΔUL/UL = ±0.1%. Consequently, the expanded relative uncertainty for the sound speed in liquid equals ±0.3% at a 95% confidence level.