|Wall chart of the liturgy in boxes with the corresponding number for each date in the period between Passover and Shavuot. The injunction to count the 49 days from the 16th of Nisan until Shavuot is considered to be at present time of rabbinic authority only. The 49 days themselves are commonly known as the sefirah.
The counting is preceded by a special benediction "... concerning the counting of the Omer."
The kabbalists used the 49 days (7 X 7) to form permutations of various sefirot denoting the ascent out of the 49 "gates" of impurity of the Egyptian bondage to the purity of the revelation at Sinai. In many prayer books these combinations are printed at the side of each day listed.
In order not to forget the count of the day it was fairly common practice to have an "Omer calendar" in the home with movable numbers on it. These "calendars" even developed into an art form and several early specimens show intricate work and lettering.