private void setVPosition(double pos) {
        // ....
        content.estimatedScrollYProperty().setValue((double) Math.round(offset));
    }

void setLengthOffset(double pixels) {
        double total = totalLengthEstimateProperty().getOrElse(0.0);
        double length = sizeTracker.getViewportLength();
        double max = Math.max(total - length, 0);
        double current = lengthOffsetEstimate.getValue();

        if(pixels > max) pixels = max;
        if(pixels < 0) pixels = 0;

        double diff = pixels - current;
        if(diff == 0) {
            // do nothing
        } else if(Math.abs(diff) <= length) { // distance less than one screen
            navigator.scrollCurrentPositionBy(diff);
        } else {
            jumpToAbsolutePosition(pixels);
        }
    }

double diff = pixels - current;