UTG19, thats a pretty big difference. I use the same Shooting Chrony and have been happy so far[about six years] Check your distance to chrony like dmazur said. I usually put it out at 12' for pistols. What gr bullet were you testing? And what charge of powder? Barrel length? These all come in to play. Make sure your screens are on if its sunny. Also, try putting a piece of Scotch tape over both of those little windows on each end of chrony. It will help.
Let us know how this works out.