This probably means there were at least two ways of measuring a shekel. This refers to how the priests of the sanctuary weigh a shekel. AT: "the official standard in the sacred tent"
# the sanctuary
This is another name for the holy tent.
# he must add one-fifth
This means the person must pay an extra one-fifth of the value of what he owes to Yahweh.
# one-fifth
This is one part out of five equal parts. (See: [[rc://en/ta/man/translate/translate-fraction]])
# the priest will make atonement for him
The abstract noun "atonement" can be stated as a verb. AT: "the priest will atone for him" (See: [[rc://en/ta/man/translate/figs-abstractnouns]])