\magnification=\magstep1


$$
(m_2 - m_1) \quad = \quad - 2.5 \ \log_{10} \left( {{I_2}\over{I_1}} \right)
$$

$$
{{I_2}\over{I_1}} \quad = \quad 10^{-0.4 \ (m_2 - m_1) }
$$



\bye