log_a(b) = log_c(b)/log_c(a) for any valid base c. Special cases: log_a(b) = 1/log_b(a), and the chain rule log_a(b)*log_b(c) = log_a(c). These allow converting between any bases. For computation, convert everything to log_10 or ln. The chain rule is particularly useful: log_2(3)*log_3(5)*log_5(8) = log_2(8) = 3.