nRF24L01+ RF_CH bits

I am confused by the channel bits in register 0x05.
why is there a '1' in bit 1. I guess it can't be used and so the range is

00000010 - 2400MHz
00000011 - 2401MHz
00000110 (6) - 2406MHz ??????
00000111 (7)

The datasheet says the freq range is 2400 to 2525MHz but it also says Freq = 2400 + RF_CH MHz
Which therefore makes the first channel (00000010) 2402MHz

I can't make sense of it

Presumably a value of 0b0000 000 in the top 7 bits means 2400 ?

It hardly matter a great deal so long as you have the same value in all the modules that need to communicate with each other.

Simple nRF24L01+ Tutorial