tvb = 0, tvb := _nvb == 0 ? nz(tvb[1]) + 1 : nvb // total volume bars in sample
tvs = nvb == 0 ? cum(volume) : sum(volume,nvb) // total volume in sample
tvb = 0, tvb := _nvb == 0 ? nz(tvb[1]) + 1 : _nvb // total volume bars used in sample
tvs = _nvb == 0 ? cum(volume) : sum(volume, _nvb) // total volume in sample