More generally, Claire, they are used by priests to bless the people at any time when the blessing occurs during the liturgy (i.e., anytime the priest says “Irnie pasi”/“Peace be with you all”, to which the people respond, variously “Ke to pnvemati sou”/“And with your spirit”/“W m’a ruhak aidan”, depending on language – just like during the Latin mass). And of course, since it is a blessing cross, it also used outside of the liturgy proper for blessing of homes and objects, during confession (the priest makes the sign of the cross over you and places it on your head while reciting the absolution), etc. It’s sort of an all-purpose item. What I wrote was my own private use (though I know other people who do it, too; I’ve seen videos of the midnight praises at monasteries where monks do the same thing, so it may have been picked up from the monks, for all I know), because during the liturgy we mark each Kyrie Eleison with the sign of the cross anyway, so I’ve gotten used to counting them this way.