There are two....err FOUR meters. (Changed to better explain)
The first is the laser throttle meter. This is showing that your laser is currently putting out and you change it up and down using your mouse wheel or whatever you bound to that control. This is the only thing you have direct control over other than turning the system on and off. I prefer binging a secondary HOTAS or other throttle for control, but if you do, make sure it has a large range of motion for fine control.
The second is the mining meter on the left hand side under the power graph. This is the graph with the white, green, and red bands, increase the laser throttle until this meter starts to increase. When it gets to the green band, back down your laser throttle to keep this in the green portion. With practice, this will get easier. If it gets into the red, either turn off you laser, throttle it way back, or move the laser off the rock. You accumulate overcharge very quickly, so depending how far into the red you get and how fast you can chip the power, it might be better to turn the laser off or move the laser off the rock. There is a lag to this meter compared to the throttle meter (by design). It represents how hot the rock is getting. In the green zone, it’s hot enough to generate forces that will split the rock. In the red zone, it is too hot and the forces being generated can blow the rock apart. Backing down the throttle will reduce the heat, it it can take time for the rock to cool off. Get it too hot and yes, it can go to fully overcharged and blow up on you even if you turn the laser off, just from residual heat.
The first...third is the fracture meter on the right hand side which is what you need to get to 100 percent to fracture the rock. This is done by keeping it in the green band. Below the green band, you do not gain fracture power and will lose somewhat quickly any fracture power you have gained.
The second fourth is the overcharge meter, also on the right hand side. This is what starts filling when you get into the red band. It goes down when you are out of the red band, but slowly. If this meter is anything but 0 when the fracture meter hits 100 percent, the rock blows up and you lose a percentage of your rock. This explosion can be violent and can damage or destroy your ship depending on how much overcharge there is. Overcharge also means the fragments go flying, which means chasing them down..especially in space
If the overcharge hits 100 percent, it blows us very violently, no matter what the fracture percentage is at. Lots of damage and high likelihood of ship destruction depending on how close you are.
If the power goes into the red part of the band, red, you need to let the overcharge meter go to 0 before it can be safely cracked. In other words, you have to let the rock cool completely down before you try again. In many cases, it’s better to find a different rock.
In some rare cases, certain rocks can’t be initially split by one prospector. In that case, it’s better to have one hold steady at a certain output, 50 to 75 percent if possible, and let the other person chase the fracture zone. Some rocks may require 3 or more people as well, but they are very rare.
New for 3.3, rocks can split so that some chunks will have a much higher percentage of ores. Pay attention to the high value chunks and let the smaller percentage ones go for best returns.
Edit: if you have a rock with a really small green band and have had a long hard fight getting it to fracture, it might be better to let it fracture with 10 percent overcharge than put yourself in another 5-10 minute battle for the initial split. I would not do that for any OC percentage over 10 and I really want it to be 0 overcharge 99 percent of the time