I keep getting the terms confused: 1) if I have the equation -Δr2+c2Δt2=s2 does one say that I am using the (-,-,-,+) signature? 2) Given the above , if s2 > 0 then the interval is space-like, and if s2 < 0 it is time-like, or is it vice-versa? 3) If I now use the proper time τ , is it the same (as far as signature, space-like and time-like) for -Δr2+Δτ2=R2? 4) If R is the space-time radius of an arc in the above, what would that arc be? Thanks for any help.