Intermediate control limits not being plotted

[johnmackintosh]

The initial periods and any sustained calculations are correct, but the plots slope down (e.g. the C chart, when the should remain constant. This is because the intermediate control limits are not being carried forward
Need to carry forward the intermediate limits between the initial limits and the first run, and any subsequent runs

• intermediate points from initial rows to first sustained row

• test for points between successive runs, but after 'look_forward' period