# C006

> subscription series is read-only

**Severity** Error

A series that belongs to a subscription (`chart.close`, `oi.value`, `funding.rate` and so on) is filled by the engine; scripts can read it with `[n]` but cannot push to it or overwrite its elements, even through another name.

Keep your own derived history in a `state` rolling buffer and push into that.

## Failing example

```flowscope
script "Smoothed closes"
data chart = subscribe(data.ohlcv)
plot avg = plot.line(title: "Mean of last 10")
on chart.close {
  chart.close.push(ta.ema(chart.close, 3))
  avg.plot(ta.sma(chart.close, 10))
}
```

## Fixed example

```flowscope
script "Smoothed closes"
data chart = subscribe(data.ohlcv)
state smooth = rolling<float>(10)
plot avg = plot.line(title: "Mean of last 10")
on chart.close {
  smooth.push(ta.ema(chart.close, 3))
  avg.plot(smooth.avg())
}
```

## Related

- [C001](/docs/scripting/reference/diagnostics/c001)
- [T420](/docs/scripting/reference/diagnostics/t420)