apexi boost gauge/egt

been on to apexi web site and can get boost gauge, indiglo, with reset buttons etcBUT all the electronic boost gauges are kg not psi? why is this and what would the differences be ie what psi relates to kg?

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95 S14
HKS FILTER
HKS DOWN PIPE
DE CAT PIPE
TRUST BL CAT PACK
GREEDY BOV

It is because its a Japanese make. They do not use the imperial system only metric. 1 kg/cm is roughly equivalent to 1 bar or 14.5 psi.

I have an electronic HKS gauge which reads in psi, but I think this was a special for the US market.