Mmmm, I think the formula is (end - start) / (number_of_parts - 1).

use strict;
use warnings;

use feature 'say';

display_parts( 0, 9, 10 );
display_parts( 0.022, 0.086, 10 );
display_parts( 0.123, 8.672, 10 );
display_parts( 1_123_345_456, 1_124_246_357.5, 11 );

sub display_parts {
    my $result = get_ticks(@_);

    printf "start: %s, end: %s, parts: %s\n",
        map pretty($_), @_;

    for ( 0 .. $#$result ) {
        printf "  %2d => %s\n", $_, pretty( $result->[$_] );
    }

    print "\n";
}

sub get_ticks {
    my ( $start, $end, $parts ) = @_;

    my $tick = ( $end - $start ) / ( $parts - 1 );

    my @result;
    push @result, $start;
    push @result, $result[-1] + $tick for 1 .. ($parts - 1);

    return \@result;
}

sub pretty {
    return shift =~ s/\d \K (?= (?: \d{3} )+ \b )/_/xgr;
}
[download]

output:

start: 0, end: 9, parts: 10
   0 => 0
   1 => 1
   2 => 2
   3 => 3
   4 => 4
   5 => 5
   6 => 6
   7 => 7
   8 => 8
   9 => 9

start: 0.022, end: 0.086, parts: 10
   0 => 0.022
   1 => 0.0_291_111_111_111_111
   2 => 0.0_362_222_222_222_222
   3 => 0.0_433_333_333_333_333
   4 => 0.0_504_444_444_444_444
   5 => 0.0_575_555_555_555_555
   6 => 0.0_646_666_666_666_667
   7 => 0.0_717_777_777_777_778
   8 => 0.0_788_888_888_888_889
   9 => 0.086

start: 0.123, end: 8.672, parts: 10
   0 => 0.123
   1 => 1.07_288_888_888_889
   2 => 2.02_277_777_777_778
   3 => 2.97_266_666_666_667
   4 => 3.92_255_555_555_556
   5 => 4.87_244_444_444_445
   6 => 5.82_233_333_333_333
   7 => 6.77_222_222_222_222
   8 => 7.72_211_111_111_111
   9 => 8.672

start: 1_123_345_456, end: 1_124_246_357.5, parts: 11
   0 => 1_123_345_456
   1 => 1_123_435_546.15
   2 => 1_123_525_636.3
   3 => 1_123_615_726.45
   4 => 1_123_705_816.6
   5 => 1_123_795_906.75
   6 => 1_123_885_996.9
   7 => 1_123_976_087.05
   8 => 1_124_066_177.2
   9 => 1_124_156_267.35
  10 => 1_124_246_357.5
[download]

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