Thank you for filing a bug for it. You are right, it should be returning numbers between 0 and 100. There must be something wrong here. I'll take a look definitely. If you see anything in the code that is not right, please do let me know as well.

Hi, is this issue resolved or is someone working on it currently? Else I would like to look into this, if its fine.

Hi Abhishek, Not yet fixed, and no active development on this as of now, so please feel free to take it.

Since this same issue was also raised in the indicator go repo. I am referring to the same resources that were pointed out there to implement this indicator.
File: projectionOscillator.ts

Our Code

const x = generateNumbers(0, closings.length, 1);
const lsHighs = movingLeastSquare(period, x, highs);
const lsLows = movingLeastSquare(period, x, lows);

const vHighs = add(highs, multiply(lsHighs.m, x));
const vLows = add(lows, multiply(lsLows.m, x));

According to the resources the pseudo code looks as follows:

Pseudo Code

//method = user defined, default is EMA
//pboPeriod = user defined, default is 14
//sigPeriod = user defined, default is 3
//index = current bar number, LOE = less or equal

mHigh = linRegLine(period, high)[1];   //returns the slope (m) of Linear Regresion line
mLow = linRegLine( period, low)[1];
count = 0;
pbw = 0, pu = 0, pl = Double.MAX_VALUE;
for (i = (index-pboPeriod + 1); i LOE index; i++)   //move back 1 period
    high = high[i];
    low = low[i];
    vHigh = high + (mHigh * (count));
    vLow = low + (mLow * (count));
    if (vHigh moreThan pu) pu = vHigh;
    if (vLow lessThan pl) pl = vLow;
    count++;
endFor
Plot1: PBO = 100 * (price - pl) / (pu - pl);
Plot2: SIG = ma(method, sigPeriod, pbo);
buy = crossedAbove(PBO, SIG);
sell = crossedBelow(PBO, SIG);

I think the error is in calculating vHighs and vLows

Possible Error

In this pseudo code, they are calculating the indicator value on each incoming bar(represented by index). So in every single window( of size =pboPeriod) they are multiplying the mHigh with an array of [0,...,pboPeriod-1]. Whereas we are mutiplying our lsHighs.m[index] with x[index].
I could be wrong here, but this is what I inferred. What do you think about this?

Also any suggestions on how I can verify the correct working of the indicator(example: sample data along with correct values of indicator)?