Conversion of wave values into positive peak amplitudes

Hello,
I am using Muse headband to measure brain waves in real time. The range of amplitude I get from the headband is between -1 to 1 for each of the five brain waves; delta, theta, alpha, beta, and gamma. What I want to do is to compare the 5 different brain waves (d,t, a, b, g) and decide which one has the highest amplitude. But before I do that I have to scale the -1 to 1 range to a positive range for example 0 to 100. I could use the [scale] object to scale (-1 +1) to( 0 - 100) but it is not as simple as that. I need to know the highest apmlitude, so if for example delta wave sends me a value of -1 and alpha wave sends me a value 0.5, numerically alpha is higher than delta but delta has more amplitude than alpha even if it is negative, however in scaling with the [scale] object -1 will be equal to 0 (I think) and 0.5 equal to 50, and 1 to 100, which in this case will give me alpha as having the highest amplitude, a different and false result. Can anybody help me solve this problem?