Calculations

[carlislewwtp]

Do not know where to start



I operate a Water Treatment Plant and I am trying to build a data base to hold our information. One task I am trying to do is everyday we write down the water meter reading for the amount of water we have pumped for the past 24 hours. I have created a form and Table to log this information. Each day is a record in the Table. I need to subtract todays meter reading from yesterdays meter reading to get a total amount of water pumped.

My coding abilities are very limited and I have been trying to use the builder function but I am not able to complete this calculation.

[orange]

Start with a clear business requirement -- a clear description of WHAT you intend to do in simple, English (no database or water treatment jargon).
What else, besides recording the daily volumes, is involved and/or will be involved with this proposed database?
Employees? Attendance? etc etc.....

Lots of database planning and design info at this link.

Good luck. (It sounds to me you are planning to build the database)

-- See the info at this Heading for meter reading info

Get the value in another record


at http://allenbrowne.com/subquery-01.html

[RuralGuy]

Could you use a DLookup() to get the previous value?

[ArviLaanemets]

Something like

SELECT 
m.MesuringDate, 
(m.MeasuringValue - (SELECT TOP 1 m0.MeasuringValue FROM tblMeasurings m0 WHERE m0.MeasuringDate < m.MeasuringDate ORDER BY m0.MeasuringDate DESC)) AS [Qty] 
FROM tblMeasurings m
ORDER BY m.MeasuringDate ASC

will give you list of quantities by dates