Operations Management - Computation of Normal Time and Standard Time for a Job

 

Computation of Normal Time and Standard Time for a Job

 

Normal time for a job =

∑ (Normal times for all the elements of the job)

 

Normal time for an element =

[(μ of Recorded Times) × (Performance Rating expressed in %-age with 100% as the ‘accepted’ performance)] ÷ 100

Note: ‘μ’ is Arithmetical Average or Mean.

 

Standard time for a job =

(Normal time for the job) ÷ (1 – Total allowance expressed as a fraction)

 

Important note:

Required number of readings to be recorded for an element (i.e. sample size of readings), for calculating standard time for a job, can be calculated as follows:

  

Nreqd =

[[40. {Ntaken∑X^2 – (∑X) ^2}^ (1/2)] ÷ ∑X] ^2

 

Where,

Nreqd =	Number of readings required to be recorded for an element for calculating standard time for a job
Ntaken =	Number of readings for the element taken, based on which Nreqd is being determined
X =	Value of the individual readings of the element

 

Illustration:

Continuous Stopwatch Time Study Figures for a job are given below. Calculate the Standard Time for the job assuming that the sample size is adequate, and total allowances are 15%.

Cycle	Elements
	1	2	3	4
	(Continuous Stopwatch Time Study Figures in Minutes)
1	0.09	0.16	0.28	0.41
2	0.49	0.56	0.67	0.80
3	0.89	0.95	1.07	1.21
4	1.31	1.38	1.49	1.61
5	1.70	1.76	1.88	2.00
6	2.09	2.16	2.28	2.41
7	2.50	2.57	2.68	2.80
8	2.88	2.95	3.07	3.20
9	3.29	3.36	3.40	3.62
10	3.71	3.78	3.90	4.03
Performance Rating	90	110	120	100

 

Solution:

Cycle	Elements
	1	2	3	4
	(Stopwatch Time Study Figures in Minutes)
1	0.09	0.07	0.12	0.13
2	0.08	0.07	0.11	0.13
3	0.09	0.06	0.12	0.14
4	0.10	0.07	0.11	0.12
5	0.09	0.06	0.12	0.12
6	0.09	0.07	0.12	0.13
7	0.09	0.07	O.11	0.12
8	0.08	0.07	0.12	0.13
9	0.09	0.07	0.04	0.22
10	0.09	0.07	0.12	0.13
μ	0.089	0.068	0.109	0.137
Performance Rating	90	110	120	100
Normal Time for Element in Minutes	0.0801	0.0748	0.1308	0.137

 

Normal time for the job

= 0.0801 + 0.0748 + 0.1308 + 0.137 = 0.4227 Minutes

 

Standard time for the job

= (Normal time for the job) ÷ (1 – Total allowance expressed as a fraction)

= 0.4227 ÷ (1 – 0.15) = 0.4973 Minutes