Power BI - Filltering dates to +/- 10 days

Hi,

I'm a reasonably advanced user of Excel but new to Power BI.

I have a large dataset consisting of temperature readings every fifteen minutes over a period of several years.

I want to filter my results to + and - ten days from the current date.

So far...

I have created a measure to determine the day no of the current date:
CurrentDayNo = value(today()-DATE(YEAR(today()),1,1)+1)

I have created a measure to give the day number for the date in my dataset i.e. the temperature readings:
DayX = value([TimeStamp]-DATE(YEAR([TimeStamp]),1,1)+1)

Finally, I tried to create a measure to subtract one from the other (which I would then use as my filter):
CurrentDayDiff = [CurrentDayNo]-[DayX]

But this last measure gives an error:
The value for DayX cannot be determined. Either the column doesn't exist, or there is no current row for this column.

Any advice much apprecated. Perhaps my approach is wrong and/or there is an easier way of filtering my results?

Thanks.