[Python] Pygame Movement Stuttering

When I try to move Surface in Pygame, it seems to stutter in a weird way. Even when I use dt, the movement speed is not constant. Even thought FPS oscilate around 59-61, the Surface sometimes moves just a few, pixels and sometimes makes a big jump ahead. Theres no visible lag, or pause between the frames. I've seen this problem occur in many Pygame projects.

I haven't found any working fix to this problem, except using higher framerate rates.

import pygame

# setup
pygame.init()
screen = pygame.display.set_mode((800, 600))
clock = pygame.time.Clock()

# start position of rect
x = 0
dt = 0

running = True
while running:
for event in pygame.event.get():
if event.type == pygame.QUIT:
running = False

# move react
x += 200 * dt

# refresh
screen.fill("black")
# draw rect on Surface
pygame.draw.rect(screen, "white", (x, 200, 50, 50))
# flip
pygame.display.flip()

dt = clock.tick(60) / 1000

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