The FBI processed more gun-related background checks this September than any other on record, documents released on Monday show.

1,992,219 checks were conducted through the National Instant Criminal Background Check System, or NICS, last month. The number represents an increase of nearly 200,000 checks, or more than ten percent, over September 2015. September is the 17th month in a row to set a new record within its month, a streak dating back to May 2015.

The FBI’s accounting of how many NICS checks were processed in a month is considered one of the most accurate metrics for judging gun sales. Virtually all sales made through licensed gun dealers must include a NICS check. Some states require sales between private parties to include an NICS check as well.

The number is not a one-to-one measure, however.

“These statistics represent the number of firearm background checks initiated through the NICS,” a note on the FBI report cautioned. “They do not represent the number of firearms sold. Based on varying state laws and purchase scenarios, a one-to-one correlation cannot be made between a firearm background check and a firearm sale.”

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