There is a calculator built into Windows.

Is this cos a = 6370 /(6370 + 0,168)? If so cos a= 0.00726. (Since 6370/6370,168 is very close to 1= cos(0) a is very close to 0.)

If cos a = 6367,5 / 6367,5015= 0.9999998 then a= 0.0006863981. Since 6367,5/6367,5015 is even closer to 1, this is even close to 0.