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The graph of Cable Head (or connector, in the case of pipe) Tension vs Depth is a companion graph to Surface Weight vs Depth, looking at the results from the downhole perspective.

Here, the predicted tension at the top of the toolstring (the blue and green lines on the far left) is usually quite small, being the buoyant weight of the tools adjusted for deviation and drag. The weak point (if there is one) shows up as two straight lines, the upper and lower ratings (if the cable head tension exceeds the weak point rating at any depth, this tells you that the weak point will most probably be broken even under normal operating conditions, which should obviously never happen). The cable breaking strength, or yield, line is not a constant (as it was in the surface weight plot) because here the line represents the cable head tension when the surface tension reaches the working limit.

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