This calculates the change in value between two dates. It is useful for studying trends in a time series. For example, unemployment trends or changes in interest rates.
ACH# has both static and moving formats:
ACH#(Expression,Start Date,End Date)
This static format calculates the actual change in value between the start and end dates. Actual dates are typed using either the standard format DD/MM/YY, or the displacement date format, for example, -NY.
As a date parameter one can also use YRE, HFE, QTE, MTE, WKE, LYE, BDATE, BDATEXXF The function type arguments MIN and MAX can be used here as well as LYE.
ACH#(Expression)
If you do not specify start and end dates, the defaults are the start and end dates for the display period.
ACH#(Expression,Period)
This moving format calculates the change in value over a time period continuously between the display start and end dates.
ACH#(Expression,Period,Parameter)
This moving format calculates the actual change for a time period continuously between the start and end dates for the display period. The trailing parameter determines how observations are selected and can have the following values.
R: Exclude “non-working” days so null values are skipped.
ACH#(J:KYTV,1/1/98,31/12/98)
This static format calculates the actual change in value for the Bank of Kyoto between 1/1/98 and 31/12/98.
ACH#(J:KYTV)
This default static format calculates the actual change in value for the Bank of Kyoto between the start and end dates for the display period.
ACH#(UKWHUNRTE,3M)
This moving format calculates the continuous actual change in the UK unemployment rate over a 3 month period. A value is calculated for each month between the display start and end dates. When used in the Graphics programs, the first value is the change between the start date and the value 3 months previously, and the last value is the change between the end date and the value 3 months previously.
You must use a time period that is consistent with the frequency of the stored data. The period frequency you request in the function can be greater but not less than the data frequency. For example:
ACH#(UKRP....F,12W)
A weekly period is invalid for the UK inflation series because the frequency of the data is monthly.
Note: You can use ACH# with a maximum of 4,000 values. If you request an actual change calculation that requires more than 4,000 values, an error message is displayed. To reduce the number of values, either reduce the display period or the actual change period. These time periods should not exceed 15 years.