Hello and thank you for your help.

I want to create a condition where OBV is above it's 21 xma by more than 15%  and another one below the 21 xma by 15% also.  I know how to do this but I do no know the expression for the obv avg.

I was doing 

XMA21(OBV) / OBV > 1.15  

BUT IT DID NOT WORK.

You can write a formula for OBV being more than 15% above its 21-period exponential moving average as:

OBV > 1.15 * XAVG(OBV,21)

And you can write a formula for OBV being more than 15% below its 21-period exponential moving average as:

OBV < .85 * XAVG(OBV,21)

But it really doesn't make any sense to do so both because the value of OBV is completely meaningless and because OBV can cross through zero. This means a percentage of the moving average is meaningless.

You might want to read through the following to get an idea about what does and doesn't work regarding cumulative indicators such as MoneyStream (MS) and On Balance Volume (OBV).

Dealing with OBV & MS in PCF's - how to interp their "values"

So you could create a condition for OBV being more than 15% of its range over the most recent 100 bars above its 21-period exponential moving average and still be creating a valid formula.

OBV > XAVG(OBV,21) + .15 * (MAX(OBV,100) - MIN(OBV,100))

With a similar condition for OBV being more than 15% of its range over the most recent 100 bars below its 21-period exponential moving average being written as follows.

OBV < XAVG(OBV,21 - .15 * (MAX(OBV,100) - MIN(OBV,100))