Distinct Row Count with filter for Transaction Amount

[astano05]

I'm looking to get the distinct count of rows when the transaction amount is below a certain value. It also will not let me place a visual level filter on the card of the count.

I try 

CALCULATE(DISTINCTCOUNT('Transaction History'[ORDER_NUMBER]),[Transaction Amount]<500) but i get this error: "A function "Calculate" has been used in a True/False expression that is used as a table filter expression. This is not allowed."

I also tried 

Order under 500 = countrows(DISTINCT(SELECTCOLUMNS('Transaction History',"under 500",[Transaction Amount]<500))); but it gives me an incorrect count. 

I have a table as below:

Order Number	customer	Sum of Order Amount
1	A	1000
2	A	250
3	A	100
4	A	600
5	B	200
6	B	1000

I want a card to show the number of orders below $500 (3). 

[amitchandak · Accepted solution]

@astano05 , Assuming Sum of Order Amount is a measure

Create a new measure

countx(filter(values('Transaction History'[ORDER_NUMBER]), [Sum of Order Amount]<500),[ORDER_NUMBER])

[astano05]

Yes this works perfectly! Thank you