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Benchmarking Process Data - Man-day calculation gone wrong

mikethepenguin

Starting to get Involved
Man-day calculation gone wrong

Dear all, whilst looking at improving a process I have used the following criteria;

1 working day = 7hrs = 420mins
Number of items processed = 1600
Time taken to process items = 7 months
Process time for 1 unit = 66minutes

1600*66 = 105600/420 = 251 man-days.

How can this process take 251 man-days when only 7 months has elapsed?!
50 working weeks * 5 days a week = 250 days per year.
250*(7/12) = 146 days in 7 months.

Does this mean in theory the person doing this task is working over-time?
105600/146 = 723mins for the day or 12hrs per day processing these items?
Can anyone offer some advice? Last edited:

howste

Thaumaturge
Super Moderator
Is only one person working in the process? Is the person able to work on more than one item at a time? (i.e. place part in fixture and start machine, then do another task on another part while it's running)

mikethepenguin

Starting to get Involved
Is only one person working in the process?
Sometimes, someone can start the process for him but not very often, from what I remember.

Is the person able to work on more than one item at a time?
Yes sometimes he can multiple items in one process step.

This an invoice processing process, the main part of the process takes 36 minutes to process 1 invoice. Then there's a delay of 8hrs over night where someone looks at the invoice, this is then sent back. If there are changes to be made the rest of the process takes 30 minutes. Putting it back to 66 minutes processing time.

howste

Thaumaturge
Super Moderator
It sounds like you're making the assumption that all invoices take an equal amount of time, but they actually don't. You said that if there are changes the processing time is 66 minutes. By logic then, if there are no changes then the processing time is 36 minutes. What percentage of the time are there changes needed?

I'll assume (as an example) that only 1 in 5 invoices need changes. Then the math would be (320*66) + (1280*36) = 67200 minutes or 160 man days. This is a lot closer to the actual time that you're showing. If you reduce it to 1 in 10 invoices you're at about 148 days.

mikethepenguin

Starting to get Involved
It sounds like you're making the assumption that all invoices take an equal amount of time, but they actually don't. You said that if there are changes the processing time is 66 minutes. By logic then, if there are no changes then the processing time is 36 minutes. What percentage of the time are there changes needed?

I'll assume (as an example) that only 1 in 5 invoices need changes. Then the math would be (320*66) + (1280*36) = 67200 minutes or 160 man days. This is a lot closer to the actual time that you're showing. If you reduce it to 1 in 10 invoices you're at about 148 days.

Thanks I was already trying to guess where your next point was going, and I have gone with the assumption that 90% pass through at 36 min with 10% taking 30 min. Extrapolated for the year results with 254 days to run the process.  