How many observations should i take to get the accuracy of arithmetic mean ̅≤ 0.1 milimetres?

#1
here is my dataset of 50 observations, all observations are in metres, mean = 23.458 metres, variance = 8.9112e-07, standard deviation = 9.4399e-04

23.4586
23.4591
23.4566
23.4578
23.4580
23.4581
23.4589
23.4587
23.4587
23.4582
23.4597
23.4577
23.4581
23.4574
23.4579
23.4587
23.4568
23.4582
23.4573
23.4588
23.4560
23.4560
23.4596
23.4579
23.4560
23.4563
23.4579
23.4583
23.4583
23.4591
23.4583
23.4579
23.4590
23.4601
23.4580
23.4578
23.4590
23.4575
23.4565
23.4579
23.4582
23.4581
23.4569
23.4574
23.4573
23.4590
23.4579
23.4586
23.4586
23.4578