Measuring SRM

I realize not many people have access to the necessary equipment to directly measure the color of a beer, but fortunately, I work in a research lab and have all this stuff sitting around, waiting to be used by curious brewers such as myself.  My most recent finished beer, an ESB, was just kegged and I've always wanted to try out the spectroscopic determination of beer color, so I though I'd give it a shot.
Wikipedia (which was the only source I could which gave the wavelengths needed for the process) defines the SRM (an acronym for Standard Reference Method - the output of the equation is in dimensionless units) of a beer as the absorbance at 430 nanometers times a constant and a dilution factor.

SRM = 12.7 * D * A, where D is the dilution factor (for an undiluted sample, D = 1, for a sample diluted 1:1 with deionized water, D = 2, 1:2 D=3, etc.) and A is the absorbance at 430 nm.

When I ran my ESB through, I got an absorbance of 1.36, which resulted in an SRM value of 17.3 -- what? An SRM of 17.3 is something expected from a dark lager, not a golden ESB. However, an EBC value of 17.3 looks right on, and conversion to SRM using the formula SRM = EBC * 0.508 results in an SRM of 8.8, which is close to the color calculated by my brewing software, 9.5.

Is Wikipedia wrong, or are my measurements incorrect? Does anyone have a reference for these measurements?

For those interested, here is my procedure:

1. Dispensed 35mL of beer into a centrifuge tube
2. Centrifuged at 10,000 RPM for 10 minutes
3. Passed supernate through a 0.3 micron syringe filter
4. Decanted filtrate to a small vial
5. Pipetted 3 mL into a plastic cuvette
6. Measured the absorbance at 700 nm (This measurement will tell you if your sample is clear of turbidity - a value under 0.039 times the absorbance at 430 nm means your sample is acceptably turbidity free)
7. Measured the absorbance at 430 nm

Results:
A(700) = 0.005784
A(430) = 1.36414