Near-Exponential VBA Conversion

The macro in this tutorial creates a near exponential variable conversion to be used for very large dynamic range input data entry . If for instance, we have to adjust a parameter from 1 to 1 million we can either make a spin button which can go from 1 to 1 million in unity steps (which would take for ever), or implement an exponential scheme.

We would like an exponential series of powers of 2 but numbers of 128, 256 or 512 are not appealing. Instead we could use a compromise electrical engineers have discovered long ago, a series such as: 100, 200, 500, 1000, 2000… etc. The last group of numbers are close enough to powers of two, have just the first digit non-zero and the rest of digits zeros. People like that. This tutorial will explain few options of creating those series using extremely simple VBA code.

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Near-Exponential VBA Macro

by George Lungu

– Charting for engineering and science models sometimes requires many orders of magnitude
flexibility and speed in adjusting the scale of the axes of coordinates.
Manual scaling using Excel’s menu is cumbersome and a macro was already developed for doing this. That macro can
independently change chart axis scales between 1 to 10000 in oscilloscope style: 1, 2, 5, 10, 20,50, 100 …)

– The problem with that macro is that it contains a fairly large array (acting as a look-up table)
which is defined within the body of the macro. That array contained 13 elements but sometimes we might need much more than that.

– This tutorial will solve that problem by introducing a similar approach in which we
combine a 3-element array with two VBA functions (Mod and Int) to achieve a practically unlimited range with a very short macro.

<excelunusual.com> 1

 

– Let’s look at the macro to the right. While associated with a button with a range of [0,12] this macro will
achieve a 4 order of magnitude variation of the value in cell B3

Dim arrScale As Variant

Private Sub Scale_1_Change()
arrScale = Array(1, 2, 5, 10, 20, 50, 100, 200, 500, 1000, 2000, 5000, 10000)
[B3] = arrScale(Scale_1.Value)
End Sub

-This macro is a little longer but it will be able to generate values in a practically unlimited range.
-The modulo function “Mod n” applied to a number extracts the remainder of the division of that number by n.
-The function Int(x) will extract the integer part of x.
-You can check that the following is true: a =m*Int(a/m) + a Mod m where “a” and “m” are an integers

Dim a, b As Long
Dim arrScale As Variant

Private Sub Scale_2_Change()
arrScale = Array(1, 2, 5)
a = Scale_2.Value Mod 3
b = Int(Scale_2.Value / 3)
[B7] = arrScale(a) * 10 ^ b
End Sub

This macro is similar to #2. Use it if you forget the function “Int” but you remember “Mod”

Private Sub Scale_3_Change()
arrScale = Array(1, 2, 5)
a = Scale_3.Value Mod 3
b = (Scale_3.Value -Scale_3.Value Mod 3) / 3
[B11] = arrScale(a) * 10 ^ b
End Sub

This macro is similar to #2. Use it if you forget the function “Mod” but you remember “Int”

Private Sub Scale_4_Change()
arrScale = Array(1, 2, 5)
a = Scale_4.Value -3 * Int(Scale_4.Value / 3)
b = Int(Scale_4.Value / 3)
[B15] = arrScale(a) * 10 ^ b
End Sub

<www.excelunusual.com> 2

Use this if you like to save some lines of code:

Private Sub Scale_5_Change()
arrScale = Array(1, 2, 5)
[B19] = arrScale(Scale_5.Value Mod 3) * 10 ^ Int(Scale_5.Value / 3)
End Sub

Use this if you don’t like to use VBA arrays:

Private Sub Scale_6_Change()
If (Scale_6.Value Mod 3) = 1 Then a = 2 Else a = 1
If (Scale_6.Value Mod 3) = 2 Then a = 5
[B23] = a * 10 ^ Int(Scale_6.Value / 3)
End Sub

All the macros are implemented in Sheet 1.
The range of the first macro is 6 orders of magnitude and the rest have a range
of 9 orders of magnitude (decided only by the spin button range: [0,27])

As an application of the previous ideas, the macros for a scatter chart axis scale change are shown below:

Private Sub Scale_X_Change()
arrScale = Array(1, 2, 5)
a = arrScale(Scale_X.Value Mod 3) * 10 ^ Int(Scale_X.Value / 3)
ActiveSheet.ChartObjects(“Chart_1”).Chart.Axes(xlCategory).MaximumScale = a
End Sub
————————————————————————————————————–
Private Sub Scale_Y_Change()
arrScale = Array(1, 2, 5)
b = arrScale(Scale_Y.Value Mod 3) * 10 ^ Int(Scale_Y.Value / 3)
ActiveSheet.ChartObjects(“Chart_1”).Chart.Axes(xlValue).MaximumScale = b
End Sub

by George Lungu <www.excelunusual.com>

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