Error bei der Kalibrierung

[S-Snowball]

Hello,

I followed this tutorial
https://www.turais.de/ein-rtl_sdr-mit-kalibrate-sdr-kalibrieren/

When I try kal -c 65 then I get this results

Found 1 device(s):
  0:  Generic RTL2832U OEM

Using device 0: Generic RTL2832U OEM
Found Rafael Micro R820T tuner
Exact sample rate is: 270833.002142 Hz
[R82XX] PLL not locked!
kal: Calculating clock frequency offset.
Using GSM-900 channel 65 (948.0MHz)
Tuned to 948.000000MHz (reported tuner error: 0Hz)
average         [min, max]      (range, stddev)
- 409Hz         [-423, -395]    (28, 7.226833)
overruns: 0
not found: 0
average absolute error: 0.431 ppm

what do I have to do to perform the calibration correctly?