OK - Here's my good deed for the day.

Here's the visual basic code to calculate the volume of water in a pond in the shape of a frustrum (ie a truncated rectangular pyramid)

This example the user can choose between any of 3 pond sizes using the PondNum variable. The PondHeight is the only other input variable.

The Pond Dimensions for each pond are defined inside of the function and can be tweaked to your specific application.

Our application, we need to determine the volume of liquor from a height reading on a daily basis for 3 different ponds.

If you want the function to be useable in all of your workbooks, you will need to define it as Public. This is easy. Just put the word "Public" in front of "Function" in the first line"

Enjoy :D

Function PondVol(LiquorHeight As Single, PondNum As Integer) As Single

'Constant Definitions
'BL = Base Length
'BW = Base Width
'TL = Top Length (at height H)
'TW = Top Width (at height H)
'H = Distance from base to the top surface of the pond measured vertically.

Const Pond1BL = 13, Pond1BW = 17.5, Pond1TL = 33.5, Pond1TW = 38, Pond1H = 4.1
Const Pond2BL = 14.19, Pond2BW = 13.95, Pond2TL = 38.25, Pond2TW = 38.01, Pond2H = 4.81
Const Pond3BL = 26.75, Pond3BW = 14, Pond3TL = 50.75, Pond3TW = 38, Pond3H = 4.8

'Area Calculations
Pond1BA = Pond1BL * Pond1BW
Pond2BA = Pond2BL * Pond2BW
Pond3BA = Pond3BL * Pond3BW

'Calculation of "Chunk" for to allow for Tangent Calculation.
'The Chunk is half of the difference between the top length and bottom length
Pond1LC = (Pond1TL - Pond1BL) / 2
Pond1WC = (Pond1TW - Pond1BW) / 2
Pond2LC = (Pond2TL - Pond2BL) / 2
Pond2WC = (Pond2TW - Pond2BW) / 2
Pond3LC = (Pond3TL - Pond3BL) / 2
Pond3WC = (Pond3TW - Pond3BW) / 2

'Calculate Pond Height depending upon Pond Number

Select Case PondNum
Case 1
Pond1HL = 2 * (LiquorHeight * Pond1LC / Pond1H) + Pond1BL
Pond1HW = 2 * (LiquorHeight * Pond1WC / Pond1H) + Pond1BW
Pond1HA = Pond1HL * Pond1HW
PondVol = LiquorHeight * (Pond1BA + Pond1HA + Sqr(Pond1BA * Pond1HA)) / 3
'PondHeight
Case 2
Pond2HL = 2 * (LiquorHeight * Pond2LC / Pond2H) + Pond2BL
Pond2HW = 2 * (LiquorHeight * Pond2WC / Pond2H) + Pond2BW
Pond2HA = Pond2HL * Pond2HW
PondVol = LiquorHeight * (Pond2BA + Pond2HA + Sqr(Pond2BA * Pond2HA)) / 3
Case 3
Pond3HL = 2 * (LiquorHeight * Pond3LC / Pond3H) + Pond3BL
Pond3HW = 2 * (LiquorHeight * Pond3WC / Pond3H) + Pond3BW
Pond3HA = Pond3HL * Pond3HW
PondVol = LiquorHeight * (Pond3BA + Pond3HA + Sqr(Pond3BA * Pond3HA)) / 3
Case Else
PondVol = 0

End Select

End Function