In this method the slope of the ground is first found out by using the clinometer or abney level

Hypotenusal allowance is then made for each tape length

$Θ$ - angle of slope measured by clinometer or abney level $AB=AB_1=20m=100\ LINK$ $AC=AB \sec Θ =100\sec Θ$ \begin{align} \\B_1C &=AC – AB_1 \\&=100 \sec Θ – 100 \\& =100(\sec Θ-1) \end{align} The amount $100(\sec Θ -1)$ is said to be hypotenusal allowance