ASPRO chronology - Wikipedia
Re: Lichenometry dating
Circa - Wikipedia Circa (from Latin, meaning 'around, about') - frequently abbreviated c., ca., or ca (and less frequently circ. or cca.) – signifies 'approximately' in several European languages (and as a loanword in English), usually in reference to a date. Circa is widely used in historical writing when the dates of events are not accurately known.