The glyph has a chance to upgrade the base value of the substat by any value within the range. If it fails to increase the substat from its current state, it won't decrease it. But if it succeeds, it will increase. By how much will depend on the range of values for that glyph. What is the range value for the 4* speed glyph?

Up until 6*, it's 1-glyph level for speed, eg, 4* is 1-4. 6* is 3-8. 

That solves it, then. The glyph's max and adding 1 speed to the already +3 is one and the same. 

So basically adding a four star glyph could give it more than +1 speed? I need only 1 speed for a fine tune and not going to risk it if it could put me over. 

So basically adding a four star glyph could give it more than +1 speed? I need only 1 speed for a fine tune and not going to risk it if it could put me over. I'm not sure what is meant by "range value?" It's a four star glyph gained from faction wars. Surely it will be adding just one point ? It's on +3 as shown and if it succeeds will add one? 

No? 

Thanks also <

In this instance - using the piece of gear you're looking into - it can only roll up to +4 with a 4* glyph, so it's impossible for you to go over. Given that 4* glyphs only have a range of +1 to +4 in total, finishing at +4 is the only positive roll you can get. 

Tl;dr you're super safe, you just might whiff on your 4* glyph a bunch while trying to get there

thanks for the help! That's what I assumed and wanted to be 200% sure as sure. I don't have any more wiggle room or speed gear now. A mistake ruins the whole CB team . I will get grinding on the waction fars.......

Yeah, when you select the glyph, it'll say 1-4. That's the range of values, that's the total (not additional) value it can bring to the base stat, an since it's already +3, it can only updrage to +4.

Yeah that was my assumption and wanted a definite answer before I ruined weeks of testing and tuning. Now I just have to wait for the dreaded green UNM for the proof it works!

Good luck!

What tune is it, if I may ask?

Myth , heiress , deacon , seeker , zavia. 

It works after weeks of tweaking and random fails on green UNM. I found this video that solved everything. I copied his speeds to the figure and confirmed it works on all elements - brutal to UNM. I get about 50M a key with bad gear / builds.  

https://youtu.be/NK4twa1zE9w

Credit to this guy and the in depth part on green speed on UNM. It solved everything! That's why I needed to add +1's and +2's on the champs for green UNM. The one tick of decrease speed on green meant seeker went before the DPS champ at times.