Yes, I forgot this type meter is spec'd percentage of full scale.
Still though, unless you are doing extreme QRP, it shouldn't matter. Most hams use it to peak the output. At that point, whether it is 120 watts or 90 watts (unlikely) technique will win pile up, not that extra 30 watts. Today's most transistorized HF transmitters (tube type tended to drop on 10 meters band) are spot on + legal allowance on overage.
At this point, it's only useful as VSWR meter.
Having said that, I am a ham, too. ONE MORE WATT.... I understand. 5% accuracy, I understand, too. By the way, I read somewhere a report from someone who bought a brand new Bird. His was no where close to 5%.