Hi!

I have a revolving counter variable that counts until 255 and then reset.

Now I need to calculate a synthetic variable with it so I have variable -shift(variable,-1) so my problem is that when variable reset that subtraction will be negative and it couldn’t be.

Any tips on how can I still make shift operation but not having that problem?

I tried with where but do not know if it will work.

Kind regards,

Roberto.

# [SOLVED] Revolving counter

**soluciones**#1

**dsr**#2

Hello Roberto,

The way I see it a simple `abs()`

function would the trick. You can wrap your expression app with the `abs()`

function as follows:

`abs(var - shift(var, -1))`

Hope this helps.

**soluciones**#3

Hi David,

If I remember correctly, the only thing abs does is return the value in positive, right?

Imagine current value 200 and previous 190; for this case it would be x = 10.

But if we put 5 and previous 255 for example, x = 250 and this would not be the correct result.

Thanks for the help.

**dsr**#4

Roberto,

That’s quite right, I did not think correctly about the revolving condition. Nevertheless, now that I have, here is an expression that I’m sure works after giving a shot:

```
a = var
b = shift(var, -1)
where (a > b, a - b, abs(255 - b + a))
```

Best,

–David