探渊者知千仞之深,县绳之数也.故守其数者,虽深必得.——战国•商鞅 《商君书•禁使》 请翻

上下文似是“...探渊者知千仞之深.县绳之数也.故托其势者.虽远必至.守其数者.虽深必得...”
故按两部分,分别译之——
探渊者知千仞之深.县绳之数也.
The abyss-explorer achieving to detect the depth of the abyss depends on the criterion (准则,较之度数、刻度number,或更符合上下文——译者注) of the lining rope hanged (hanged,悬挂的,县,通假字,同“悬”).
守其数者.虽深必得.
Thus the depth is definitely to detect strictly complying with (遵照、遵守) the criterion (准则,同上).
这里,守（遵守,遵照）还可表示为following、in accordance with
Quoted from the Chapter To Forbid in the Book of Shangjun by Shang Yang in the Warring States period in ancient China.
有相当难度,外行抛砖,仅供参考

测量深潭的人能够知道八千尺的深度是运用了悬绳测量法
。掌握了测量方法即使非常深也一定能测出来。