Example of using simple range statistics: You run a sample on all 5 instruments and note the difference of largest and smallest result = range. You can convert this range to an estimate of standard deviation https://influentialpoints.com/Training/using-range-to-estimate_sd.htm. If you need an acceptance rule you must first define a target for this sd (= range) and a suitable coverage factor (to correct for random extreme values, e.g. 1.5) for the range. So if your results sd (range) estimate is smaller than 1.5* target sd (range) you are OK. Numeric example: Calculated range from 5 parallel samples is 10 units and you say that the acceptable sd is 4.0 units. From table https://influentialpoints.com/notes/n3ble01.htm you see that the sd estimate is 10*0.430 = 4.3 (5 results) that is over your criteria. But you realize that there could be random extreme values ("outliers"). The range estimate from sd for 5 results is 4.0/0.430 = 9.3. You multiply this range with a factor of 1.5 and get an accepted range of 14 units. As long as the range of results is under 15 you can accept the results.