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SRM Power/Watt Meter 7900 Standard
The SRM Power Meter 7900 standard uses the DuraAce 7900 chainrings, so you don’t lose any of the power you’re trying the measure.
What you lose (gain) with the SRM 7900 power meter crankset is some weight— the power metering cranks and the head unit together add about 1/2 pound to the bike weight.
Shimano specifies 725 grams for the DuraAce FC-7900 crankset with bottom bracket. SRM specifies 910 grams for the same, a gain of 185 grams, or 0.41 pounds.
Add in 2.5 ounces for the Power Control 7 head unit and mount, and you’re at 0.56 pounds extra weight on the bike. Figures might vary slightly, depending on accuracy of the specifications from both manufacturers.