offset(src, num, _id) {
        if (src.__id__) {
            src.__offset__ = num
            return src
        }
        let id = this._tsid(_id, `offset(${num})`)
        let out = ts(src, id)
        out.__offset__ = num
        return out
    }
Shifts TS left or right by "num" candles
@param {number} num - Offset measured in candles
@return {TS} - New / existing time-series