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    use List::Util qw/sum/;
    $header{"Number of Drills"} = sum
            map $_->count,
            map { values %{ $_->tool } } @drill_arr;

    timethese(-6, {
        'sum' => sub {
...
            } };
        },
    });

Benchmark: running sub, sum, each for at least 6 CPU seconds...
       sub:  7 wallclock secs ( 6.00 usr +  0.00 sys =  6.00 CPU) @ 15
+883.17/s (n=95299)
       sum:  6 wallclock secs ( 6.02 usr +  0.00 sys =  6.02 CPU) @ 40
+993.85/s (n=246783)