The difference between lg and log is that lg is a logarithm based on 10, that is, log 10A=lgA(lg is short for log 10).
Use the basic conversion formula for conversion, such as lognb = LGB/LGN.
Let 1.02 20 = m, then: both sides take logarithm (lg), and LG 1.02 20 = lgm, that is
20lg 1.02=lgm
20=lgm/lg 1.02
20=log 1.02m (based on the logarithm of 1.02)