It technically still “roughly” in case of “extra time per word”, but it is exact for other timer. Because words have different sizes it’s closer to “extra time per average word”, for example it will not spend as much time on word “I” but spend longer on very long words. After testing I found that to be much more accurately match the reading speed after adjusting without the need to manually advance because it takes too long or rollback because I couldn’t read it fast enough. But it generally pretty accurately represents how long it will take for average sentences per word.