Sail luff lengths

I think the main reason to ditch measuring a hi tech downhaul tension measurer is that the best sailors will still rig their sails on looks on the beach and then they/we adjust on feel, tweaking tensions a bit having tried the rig on the water.

Plus the downhaul tension required actually does vary from mast to mast - because bend curves and stiffnesses do vary in manufacture, even where you think you are buying an identical product.
The first principle for all rig and board tuning is that it works for you, and not that it conforms to some tape measure setting or other measured load.

The other issue with a downhaul tensioner would be where to fit it.
It can't go between the extension and the sail without lifting the rig off the deck or without adding new weight to the rig.
You also can't simply measure the load on the downhaul line tail as you tug it - because that loads varies according to whether you are using a 1:4 purchase, or a 1:6 etc... There are then friction and other issues with all sail pulleys and with the various extensions we use.

So back to basics here.
Ditch the tape measurement systems and factory settings, and learn instead to rig your own sail with the mast and boom you have.
All the measurements given are just starting points anyway, and are there for an average sailor weight on a standardised mast. If you are heavier or lighter - or use a third party mast - then those measurements probably won't be right.

At the Ezzy factory they use a load tensioner when downhauling the sail and put a biro mark on the sail before setting the gauge to the correct place. The 5 Ezzy sails I have with the system I have checked the the downhaul gauge at the foot against the marks on the leech and all 5 were spot on, and still are when they got to 100 sessions. My preferred settings are always max downhaul and outhaul, or 1cm less outhaul if its a bit light. Or if the water is flat, add 1cm downhaul for top speed. The slight tweaks I came to were after I used the sail a few times, with a GPS.
So each time I rig the sails, its easy to get it spot on each time without looking at at marks on a flapping leech .
Before I got all Ezzy masts, I calibrated the gauge against the marks on the leach. I dont know why other brands dont do something similar. I think Duotone might on their Warps, I saw Pierre Mortefon on a windsurf.tv video using a hole in the luff tube at the bottom of the mast.

Many years ago some magazines tested Ezzy sails and rigged along the same lines as other brands, more downhaul and floppy leeches, not enough outhaul, then proceeded to mark them down. They were rigged wrong. Ezzy told magazines to stop testing his sails for a while, until they got the hang of them. Which is why its important for magazine testers and sailors to rig according to the specs. If the specs given are wrong, then thats a problem, and if they thing the specs are out contact the brand. That was a long time ago, 2005 +/- a few years?? Maybe Basher can comment, he was a tester briefly around that era.

If a brand decide one year to build their sail with less downhaul, tighter leach, how is the sailor supposed to know the desired settings? Buy a secondhand sail from a few years ago, can you remember what they said at the time? It might help if brands got the specs on a sail right, and sailors actually measure their extensions. It should be idiot proof, its not complicated.

I was indeed a test editor at Windsurf magazine for a while, but I only tested boards and not sails - because I also worked for a sailmaking company and so it was considered I'd have a commercial bias in testing sails.

There was a thing about Ezzy sails at the time, and indeed some poor tests led to the sails being withdrawn from tests in several magazines.
You could argue that the testers didn't know how to rig the Ezzy sails correctly - or you could argue that those sails stood out as different and not always in a good way.
If I'd written about them at the time I'd have pointed out that those sails were cut with a lot broadseaming to give the notable fullness at the luff, and they bucked the trends of sails having batten rotation and with loose leeches at the head.
On most rigs then and now the luff curve is cut to give a deliberate mismatch with the mast bend curve and that mismatched curve results in the sails have battens which sit to one side of the mast when at rest. The wind in the sail then uses that rotation to put fullness in the sail, and that rotation also means when you sheet out the sail depowers or 'feathers' by going flatter.
The lack of rotation in Ezzy rigs meant the sails would not depower on the wave face or when feathered because the luff fullness was always there, like with a cambered sail. The plus side of that broadseaming fullness is that the luff keeps driving forwards even when overpowered.

Fifteen or twenty years on, our wave sails are still mostly rotational but you'll often find a bit of subtle fullness cut in the luff panels via broadseaming. (My Severne Blades and S1s have that whilst still being predominantly rotational sails ).
Ezzy sails remain very popular whist retaining their unique look and they also depower at the head better nowadays. The newer versions also have a different way of depowering at the luff, because they use the old 'soft sail' idea where you take out the full length middle batten(s). So the Takas depower with a fold of cloth that sits behind the mast when the sail is sheeted out or feathered.

I'm so confused to why some find it so hard to work out. If the sail says luff 490 and you have a 490 mast set the extension as short as you can, if you have a 460mast set the extension to 30cm. Try it like that then maybe a 1cm either side and see what works for you.
that gauge on the ezzy seems point less why not say downhaul until the bottom of the sail lines up with the bottom of the extension for example. You don't need another marker.

MikeyS, your attempt at poetry is comparable to you lack of extension knowledge.
piss poor.

Just measure how much you need on the extension and remember whatever number that matches up to. Or just mark the extension at the right place then you have to remember anything

Good one, the bottom is a SDM, but 10 is 10.