### Instruction:

Extract the cause and effect entities from the following sentence:
However the main drawback is that it is difficult to precisely record the arrival time of radio signals, since they travel close to the light speed

### Assistant:

KEYWORD: since
VARIABLE: the arrival time of radio signals
CONDITION: is difficult to precisely record
CAUSE_1: they travel close to the light speed
NOT_RELEVANT: However the main drawback is that it
EFFECT_1: is difficult to precisely record the arrival time of radio signals

