How do I get move_and_slide to move by one-meter intervals?

Question

extends KinematicBody

var vel = Vector3.ZERO
var frame = 0
var countingFrame = false

var gravity = 200
var speed = 200

onready var groundCheck = $GroundCheck

func _ready():
    pass

func _physics_process(_delta):
        vel = Vector3.ZERO
    frame += 1

    if frame > 15:
        frame = 1
        countingFrame = false

    if Input.is_action_pressed("forward") and frame % 15 == 0:
        vel.z -= speed
        countingFrame = true
    if Input.is_action_pressed("backward") and frame % 15 == 0:
        vel.z += speed
        countingFrame = true
    if Input.is_action_pressed("left") and frame % 15 == 0:
        vel.x -= speed
        countingFrame = true
    if Input.is_action_pressed("right") and frame % 15 == 0:
        vel.x += speed
        countingFrame = true


    move_and_slide(vel, Vector3.UP)

    print(str(translation))

    if Input.is_action_pressed("ui_cancel"):
        get_tree().quit()