Axis TCL code - bugs?

# purpose?
# gets two numeric strings, returns an index
# last return stmt out of bounds of s1
proc places {s1 s2} {
    # returns index of last int digit of s1
    #     when s1 > 1 (numeric gt op if s1 is numeric)
    #     and integer part of s1 and s2 differ
    if {$s1 > 1 && int($s1) != int($s2)} {
        return [expr {[string first . $s1]-1}]
    }
    set l1 [string length $s1]
    set l2 [string length $s2]

    # iterate s1 and s2 starting at pos 15, till end of shorter string
    # why start @15? -> val2vel formats with %32.5f so there's a bunch of leading spaces
    for {set i 15} {$i < $l1 && $i < $l2} {incr i} {
        set c1 [string index $s1 $i]
        set c2 [string index $s2 $i]

        # return current index
        # when
        #     s1 @ idx isn't a 0 or decimal sep
        #     s1 and s2 differ @ pos

        if {$c1 != "0" && $c1 != "." && $c1 != $c2} { return $i }
    }

    # just return the len of s1
    # all other return values are related to 0-based positions
    # is this intentional or -1 is missing?
    return [string length $s1]
}

# purpose?
# translates slider val to speed value
# but wiggles the slider val slightly left and right and
# decides what value to return based on 'places'
# bugged, last_... never set / prev_... set but not used
proc val2vel_show {val maxvel} {
    # translate slider value [.0, 1.] to speed value
    set this_vel [val2vel $val $maxvel]
        
    # prep some vars
    set next_places 0
    set last_places 0
    
    # get speed value and 'places(current vel, offseted vel)' when offsetting slider by 0.005
    #     to the left if possible -> next_...
    #     to the right if possible -> prev_...
    if {$val > .005} {
        set next_vel [val2vel [expr {$val - .005}] $maxvel]
        set next_places [places $this_vel $next_vel]
    }
    if {$val < .995} {
        # this should be last_... there is no prev_...
        set prev_vel [val2vel [expr {$val + .005}] $maxvel]
        set prev_places [places $this_vel $prev_vel]
    }

    # compare 'places' and return adjusted string
    # last_places still is 0
    if {$next_places > $last_places} {
        string trim [string range $this_vel 0 $next_places]
    } {
        string trim [string range $this_vel 0 $last_places]
    }
}