The top line should be at such a height that it extends past the bottom line plus two inches - including the height of an average flame from said candle.

Why 2 inches?

The centre of a 1320 foot piece of an "ideal" sphere of radius 3,958.8 miles is only about

^{1}/

_{8} of an inch above a straight line joining the ends.

And on the practical side, Dyneema (Ultra High Molecular Weight PolyEthylene) has close to the best specific strength of any fibre.

*Sufix 832 Braid Line-600 Yards* is 600 yards is a braided line with 7 Dyneema fibres plus 1 "GORE Performance Fiber".

It has a nominal breaking strain of 20 lbs and the 600 yards only weighs about 5.1 ozs.

The

**"Displacement Cable Sag Error Calculator"** needs:

the

*cable tension* in pounds force, so start at

**20** lbf, the length in feet,

the length in feet, so

**1320** feet, and

the

*cable weight per unit length*, so use

^{5.1 oz}/_{(16 × 3 × 600 yards)} = 0.000177 lb/foot.

Using these values in the

*Cable Sag Calculator* the sag in the centre of that 1320 feet is

**1.93** ft!

Maybe someone could check these figures.

In practice a 20 lb braid line will commonly not break at under twice the rated strength so let's "stretch the friendship" and put 40 lb tension on the line.

The sag is still

**0.96** ft so I don't hold any hope of measuring the "earth's curvature" that way.

And don't think that longer distances will help because over a mile that cable would sag about

**15** feet even at the 40 pound load.

Maybe someone could try it out at the 20 pound tension and 1320 feet. The line is $51.40 at

**Amazon: Sufix 832 Braid Line-600 Yards**.