Yet Another Post-Ferm Refractometer Question

[Lazer Wolf Brewing]

I'm trying to figure out how to calculate FG using the refractometer and I'm getting different numbers from different online calculators. Is there a general consensus on which calculator is most accurate? I am using Original Brix: 17, Final Brix: 9, and if there is a section for correction, I am using 1.040:

On http://seanterrill.com/2012/01/06/refractometer-calculator/
Original Gravity: 1.067
Estimated Final Gravity: 1.016
Alcohol by Volume: 6.5%

http://www.brewersfriend.com/refractometer-calculator/
Original Gravity: 1.067
Estimated Final Gravity: 1.016
Alcohol by Volume: 7.0%

http://www.northernbrewer.com/learn/resources/refractometer-calculator/,
Original Gravity: 1.065
Estimated Final Gravity: 1.014
Alcohol by Volume: 7.2%

http://www.onebeer.net/refractometer.shtml
Original Gravity: 1.070
Estimated Final Gravity: 1.014
Alcohol by Volume: 7.3%

Its weird to me that the OG's are almost all different when I used a starting brix of 17 for all. It's also weird to me that OG and FG are the same for the first two examples, but the abv is off by 0.5%.

Can someone tell me what I am doing wrong, or even better, tell me which site to use For the record, with my fermentation system, using a refractis much much easier than a hydro, hence why I am trying to make it work! Thanks as always guys.

 

[AZCoolerBrewer]

After reading a lot about this topic on HBT I would trust Sean Terrill, but I have no experience with actually applying the information.

 

[Lazer Wolf Brewing]

I'm definitely leaning towards that one, or the brewers friend one. I really don't want to use the hydro but it seems like if I want accurate numbers, I'm going to have to.

 

[Singletrack]

My calcs give 1.067, 1.016, and 6.7%

My formulas are from various sources researched years ago. If I were to use a calculator, I would use one of the first two.