How to remove fields from appearing in my timechart panel?

i'm trying to remove field from the timechart panel eg: `index=os host=xyz | timechart avg(usedMB) as DiskUsed avg(freeMB) as DiskFree avg(sizeMB) as DiskTotal by host |evalDiskUsed = round(DiskUsed/DiskTotal*100) | fields - DiskFree, DiskTotal` when i execute the above search, i see visualization DiskFree, DiskTotal too towards right end of the panel.. i want to see only DiskUsed.. How do i remove DiskFree, DiskTotal values.. help with the search..