There where some forms left in Gwoyeu Romatzyh and abbreviated spellings that I needed to investigate on.

Gwoyeu Romatzyh is a fairly complex Romanisation. Instead of using diacritic marks or appended digits, the creators decided to give each syllable-tone combintation a distinctive shape. So syllable guo (e.g. 国, 果) becomes guo, gwo, guoo, guoh for tones one to for.

This is actually the most prominent feature GR is known for. By the way, I believe it is mostly abbreviated as it's difficult to remember the correct spelling Gwoyeu Romatzyh, which itself comes from Guóyǔ Luómǎzì, "National Language Romanization", and would be strictly rendered as Gwoyeu Luomaatzyh in its own system.