Changing waveform speed to match tempo

Hi,

I'm trying to match the tempo of my patch to any waveform imported through the buffer. I thought that I had done the correct math to do this but it doesn't seem to work. I'm using waveform~ to calculate the length of the file, and divide that by the amount of bars it is long * my tempo. I then output that into a sig~ 1 which then goes to my groove~. I was certain this would work. Would it and my math is just wrong, or am i just wrong in thinking it would work

Cheers