You read Schwab right but Schwab got it wrong. Also, Arcam's language is consistent with offering a total of 4,109,286 ordinary shares when they say that 5 subscription rights allows one to buy 1 new ordinary share. The original notice reads-
Register for free to join our community of investors and share your ideas. You will also get access to streaming quotes, interactive charts, trades, portfolio, live options flow and more tools.