# Adding a custom indicator to Watchlist

Ok, let’s imagine, you have created a custom indicator and it works correctly when you add it to the ‘Chart’. But you want to add it to the ‘Watchlist’ panel too. Yes, Quantower supports this [**feature**](https://help.ampfutures.com/trading-platforms/analytics-panels/watchlist#indicators). Open ‘Watchlist’ -> click on ‘Indicators lookup’ -> and… you can’t find it. Hmm, something is wrong. And two questions come up: *“Why I can’t see it on the list?”* and *“How can I add my indicator to the list?”*.

Well, the reason is that your indicator doesn’t implement special **"IWatchlistIndicator"** interface. This is the marker which is used for filtering content into ‘Indicators lookup’ in ‘Watchlist’.

```
public class Best_Indicator : Indicator, IWatchlistIndicator    {    	… Best_Indicator code.    }
```

**For example:** Quantower platform has the built-in "*Price Action Zones*" indicator. It’s designed only for work on the ‘Chart’ panel because it uses [**custom drawing**](https://help.ampfutures.com/trading-platforms/quantower/quantower-algo/indicator-with-custom-painting-gdi). It doesn’t implement this interface, and you can’t use it in the ‘Watchlist’.

Ok, let’s remember. Before adding the indicator to the chart you need to select ‘[**TimeFrame’ and ‘Depth of history**’](https://help.ampfutures.com/trading-platforms/analytics-panels/chart/general-overview#chart-top-toolbar). But after adding an indicator to the ‘Watchlist’ you can customize input parameters and timeframe only. Hmm… “How does the Watchlist understand how deep the history needs to be downloaded?”.

![Input parameters of any indicator on Watchlist panel](https://gblobscdn.gitbook.com/assets%2F-LD6FsRvQ3jgwJIg6O7r%2F-LXUbL9piMW1EKXqd0-r%2F-LXUbk0mNpKEG6uPyobR%2Finput%20parameters%20of%20indicatos%20on%20watchlist.png?alt=media\&token=803ad4bc-ceb2-4ac9-8cfb-63a0c925dec4)

**‘IWatchlistIndicator’** interface provides ‘***MinHistoryDepths***’ property which must return a minimal history depths value for the current indicator. You need to implement it correctly and that’s all.

```
public class DoubleSMA: Indicator, IWatchlistIndicator    {        [InputParameter("First SMA period", 0, 1, 999, 1, 1)]        public int FirstPeriod = 5;​        [InputParameter("Second SMA period", 1, 1, 999, 1, 1)]        public int SecondPeriod = 10;​       public int MinHistoryDepths => this.FirstPeriod  + this.SecondPeriod ;​       … DoubleSMA indicator code}
```