LDIF calculates the difference between the current value and the last entered value of a specified variable.  This function has an optional rollover input, which can be used to specify the point at which a meter reading rolls over (to zero). 

SYNTAX:

LDIF(Vx, Optional Rollover)
where :
Vx is a conditional variable x
Rollover is an optional parameter that specifies the Rollover Point

NOTES:

This value will only search back 183 days for a previous value. 

EXAMPLES:

V96 = LDIF(V71, 1000)

Variable 96 will calculate the difference between each value of variable 71 and the previous value of variable 71 and store it on the day of the first value being compared.  The calculation will expect a rollover point at 1000, as if looking at a meter entry which rolls over. The values in variable 71 can only be separated up to 183 days (about 6 months); otherwise, no calculation will take place.