# Re: [TCML] Spark Length Measurement Techniques

Here's a scheme that I use to tune a coil to it's maximum spark length which also yields an accurate measure the length achieved. I tape a nylon weed-wacker line to the toroid and attach the opposite end to a vertical support about 20 feet from the coil. Suspended from the line are about 20 movable wooden dowels each pierced by small nails at the lower end with the nail furthest from the coil being grounded. An arc from a breakout point on the toroid will jump from nail to nail to reach ground and so you just keep increasing the dowel spacing an readjusting the coil until the arc cannot reliable span the distance. Once the coil is tuned to achieve a maximum spark length, all one has to do is measure the span and subtract the total length of the nails.
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Here's a picture this setup taken at Greg Leyh's Nevada Lightning Laboratory last summer:
```http://www.teslacoiling.com/firingthegap.jpg

Dave

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I certainly understand that references are needed and this can be done to a degree, but with sparks, this gets tricky. In order for the spark to be accurately measured via a photograph, the spark "must be" perpendicular to the camera. Even a few degrees into the Z axis, and the "object of reference and known dimensions" must be reduced in size by the angle. All sparks that have any angle to the camera from the perpendicular will always make the sparks shorter than they actually are. 13M did not have a single perpendicular arc in the photo taken. The only arc close is the one on the right that issues from the back and curves around the coil forward. If you measure with some known reference object, you still completely miss the Z axis length. I don't believe this to be the claim photo as I've already stated in the other thread, but represents my point regarding Z-axis. Not only with the angle the spark issues, but also it's curvature in that direction.
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The best way of course is to never rely on a photo as the measurement, but rather a measured "target" the coil arcs to within a photo. Spark length claims without a photo are not proof, but this doesn't mean the claim is false. It simply means you must take the claimers words with faith that it is true or not.
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My little coil 4.5"D x 21.165"H max spark length is 55" to a target. At my front page of my website is a photo of this coil and an arc (top right).
```http://www.classictesla.com/

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The two toroids edge to edge nearest distance is 55" measured with a tape measure. If you were to use a little stick man or other 2D object, what would you estimate the distance to be? For reference, the toroid on the little coil is 6.25" x 21".
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