Making and calibrating a disappearing filament optical pyrometer

So aside from the fact I can get a digital pyrometer off Ebay for $55 that can supposedly read up to 1800 deg C, I was thinking of building a disappearing filament optical pyrometer (I believe Metallab did this and has details on his website) by getting one half of a pair of compact binoculars and mounting a lightbulb at the focal point and then a dark filter before the eyepiece and a mask on the objective lens to view a small spot only. You then have a moving coil/needle type milliamp meter wired inline with the bulb to measure current with a scale to read the temperatures off.

This would need calibration from a expensive high temperature calibration source. So I was looking around online for the typical temperatures of a tungsten filament lightbulb and found this tungsten resistance chart online: it give a ratio based on the filament resistance at room temperature being 1000 and then resistances at temperatures up to 3655degrees Kelvin or 3382 deg C.

So you just measure the cold resistance of a mains lightbulb at room temp, then power it up and measure the voltage applied and then the current drawn to calculate the resistance at that power setting.

Resistance = Volts / Current then divide that value by the cold resistance, then multiply by 1000 and look up the temp on the chart (in theory...maybe).