LM567C: Center frequency is not in the expected range

Part Number:LM567C

I have set up a two tone decoder to detect 120kHz and 90kHz.

The values of the externel components of the center frequencies are calculated based on the  f0=1.1/ (R*C) formula

measuring the free running frequencies does not give the expected results. Measured @ Pin 5 oder pin 6 always results in 105kHz for the 120kHz decoder and 80kHz for the 90kHz decoder.

What am i missing here?

Furthermore in the datasheet it states that the maximum free runnning frequency is between 100kHz and 500kHz. From what is this dependent? In what conditions will it be 100 kHz

Thanks for your support in advance

greets oli