Your fuel load is whatever mode you set under Basic Setup > Engine and Sequential Settings > Control Algorithm. This is the method used to determine engine load.
You can see that in the project I pulled up (randomly), the algorithm is set to MAFMAP. That means the MAP as calculated with a MAF sensor. Most applications use speed density, which uses MAP straight off a MAP sensor.
There are also other modes such as alphaN (for big cam or big/multithrottle N/A cars that don't make vacuum), MAF, and ITB (blends speed density with alphaN; a little more work to tune than alphaN but works awesome).
The Y axis "%" value will then vary with which algorithm you have chosen. With speed density, the values represent MAP. With alphaN, they represent throttle position, etc etc etc.
Note you can use the same control algorithm for both fuel and spark, or you can run different algorithms. For instance, you could run fuel off MAF and ignition off speed density if you wanted. Some would argue that it would provide for a more accurate tune. But I bet most would argue that it would just be more work.