Hi, I set up rrd4j charting with OH2 on raspberry pi

I can chart sensor data which is coming to oh via mqtt.

but when I calculate a new item in OH rule, the new Item can not be charted.

my Item is like this:

```
Number h4 "[%.1f]"
Number t1 "[%.1f]"
```

rrd4j.cfg:

```
openhab.def=GAUGE,90,0,3,60
openhab.archives=MAX,.5,1,1440:MAX,.5,5,2016:MAX,.5,15,2668
openhab.items=*
```

persistence:

```
Strategies {
everyMinute : "0 * * * * ?"
everyHour : "0 0 * * * ?"
everyDay : "0 0 0 * * ?"
}
Items {
* : strategy = everyChange, everyMinute, restoreOnStartup
}
```

t1 is coming from temperature sensor and can be charted

but h4 is calculated by t1 â€¦and can not be charted,

the formula which calculate h4 is sth like this:

```
val edw = [ t |
var denominator = 240.97 + t
var numerator = 17.502 + t
var exponent = numerator / denominator
var pow = Math.pow(Math.E, exponent)
return 6.112 * pow
]
val Number t2Var = t2.state as Number
val Number t1Var = t1.state as Number
val ed44 = edw.apply(t2Var)
val ew44 = edw.apply(t1Var)
val numeratora = 1 + .00115*ew44
val numeratorb = ed44-ew44
val numerator = edw44 - 0.6687451584 * numeratora * numeratorb
val div = numerator / ed44
h4.postUpdate(div * 100)
```