In practice,the fact has found that the concept of continuing what comes before and enlightening what goes after,learning first and guiding second,question asking after discussion,evaluation after student\'s feedback and resource sharing should be insisted on teaching so that the vigor of class would be aroused and teaching target be achieved efficiently.

In comparison with the design parameters of the leading mark alternative of an as-built port and on the conditions of not changing the leading range and front leading mark conditions, 5 supplementary alternatives which try to adjust the space of the front and back leading marks and elevation of the back leading mark are provided, with relevant parameters calculated and compared.