Namekian fusion.

[Spyderjsr]

Another big problem however is... What in the hell determines a Power Level? What is the unit used? What is the formula to decide someones power level? Without knowing these kinda things you cant really even make estimates on power levels. Cause yea... Goku trains for three years... how? What does he do? Weight training? Gravity training? Or jus sparing? There are just so many variables that it can really make your brain start to hurt.

[Deus ex Machina]

Doesn't the anime, at some point describe how the scouter made it's estimates? Based on the fighters appearance and current Ki level?

[Dayspring]

I think it was muscle tone (appearance, like you said) and Ki, which is why so many broke: Earth ppl could change ki as they wish.

Also, in the Boo saga, the unit of measure is in "Kilis".

The 24th+25th budoukais make the easiest to analyze, but thanks to Human weakness+inferior technology, makes it totally useless for the rest of the world. I'm talking of course about the famous Punch Machine.
The Punch Machine used a recoil system, so the more it recoiled when you struck it (strength) the more Punch Machine Points you got.

[Xyex]

Are you sure? Rikuum's and Burter's power levels were similar, yet the difference in speed was obvious.

Speed training can boost you're speed a bit more than just your PL gives you. That's the opposite of being slowed down by musscle size. Everyone calls the USSJ forms useless cause of their size but if the Z fighters had trained in them long enough to get used to how they moved they could have restored their speed. Brolly was massive but still fast because he was used to the size.

[Izlude]

Maybe speed magically beomces faster with power level increases in some cases, I mean let's look at all the times Goku just vanished and then suddenly appeared OUT OF NO WHERE in the original DragonBall, the stronger Raditz appears in Z and is somehow able to go BEYOND that! Then Nappa and Vegeta can go even further beyond! And then Burter! Don't get me started with Freeza! He is like

*zip

*zooSH*

*Woooochu*

But it doesnt end there! Oh no, they just keep getting faster! How you can go so fast beyond the naked eye can see...we'll never know...but surely they are moving faster than light as early as the 23rd World Tournment

[oponok]

Power levels are too vague later on to know for sure who's how strong. At the beginning of the android saga, Piccolo is apparently in the millions since Krillin or Gohan claims he's like a Super Saiyan. But how high in the millions? We don't know how strong the androids are. And if Piccolo got that strong in just three years, who says Tien isn't at at least a million? Who can honestly tell me I'm wrong, since 1 million is no different from 125,000 when the androids may be 5 or maybe 12 million, and with Cell being 50 million or 200 billion or something. You're still as good as f***ed.

We can make up stuff, but it's rather silly to think you can come up with the explanation and theorize what their power levels are. All we know is that Piccolo dominates first stage Cell, powered-up first stage Cell dominates Piccolo even more, 16 makes powered-up first stage Cell look like a bigger pansy, second stage Cell pounds the raging hell out of 16, Vegeta smacks around second stage Cell like there's no tomorrow, so on, so forth. We don't know how much more energy someone needs to be able to kick another guy's ass, since Vegeta can punk-slap Goku when he's only 13,000 power level units above him, but Goku has a hell of a time fighting Freeza when there's a 3,000,000 difference. It's two different situations, I know, since Vegeta was three times stronger than Goku back in the Saiyan saga, but 3 million is a considerable difference. If that's so insignificant, how many millions does it take to be able to have total control during a whole fight?

Power levels past the Namek saga are impossible to even contemplate. You can guess all your want, but in the end, none of us can come up with a right answer.