Dear all!

Oh gosh, those units… only troubles…

I wanted to do a linear interpolation `y = k * x + d`

, where [x] is a temperature and [y] is a number, so I set

```
val QuantityType<Temperature> x1 = -10|°C
val QuantityType<Temperature> x2 = 5|°C
val Number y1 = 6
val Number y2 = 2
var Number k
var Number d
```

then I did

```
k = (y2 - y1) / (x2 - x1)
logInfo("test.rules", "k: {}", k)
```

and the log file gives me nicely:

```
k: -0.26...67 1/°C
```

in units 1 over °C, as expected

calculation of the offset d (done by `d = y1 - k * x1`

) involves the product `k * x1`

which proves to be problematic:

```
m = k * x1
```

gives me an error

```
Error during the execution of startup rule: °C is non-linear, cannot convert
```

despite [k] is 1 over °C and [x1] is °C, so the multiplication of 1/°C with °C should yield a dimensionless number.

what am I doing wrong here?

Thanx for support

Sulla