A good summary of the measurement issues faced when sizing up Rusia’s overall defennce stregth, published in the UK Defence Journal by J. Vitor Tossini
“According to the most recent estimates using market exchange rates, the British defence budget surpassed Russia’s in 2020 and continued to grow faster than the Russian in 2021. However, a different scenario is found when considering the Purchasing Power Parity (PPP). Although with its own limitations, this conversion method might be helpful for the governments within NATO to understand the size of the Russian defence budget.”
militaryppp.com 