Not always up. The classic counterexample is if the muzzle is too close...

...to the chrony and the gun is producing a very smokey muzzle blast. Because the blast travels faster than the pellet for the first few inches, it sometimes happens that the blast races ahead of the pellet and "trips" the front chrono sensor prematurely. This means the timer in the chrony measures, not the true time of flight of the pellet between the sensor, but instead the difference between the arrival of the blast at the front sensor and the pellet at the rear sensor.

The result is an anomalously LOW velocity reading.

Also, if the pellet's path is at an angle to the axis of the chrony (either up/down, side/side, or both), the result can be a low reading.

But check out my "altitude" post below.

Steve