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Hi,
In the article “Using Weather Adjustments” are errors in the Zimmermann formula section:

Summary of formula: Watering Percentage = (100 + (T-70)*4 + (30-H) – 200*(P-0)) %
Should not contain numbers but the base variables (BT, BH, BP)
Summary of formula: Watering Percentage = (100 + (T – BT) * 4 + (BH – H) – 200 * (P – BP)) % = 112%

Example: let’s say yesterday’s T, H, P are 86 F, 68%, and 0.12″ respectively.
Humidity value used in the calculation below is not 68 but 58
Example: let’s say yesterday’s T, H and P are 86°F, 58% and 0.12″ respectively.

the final formula is: Watering Percentage = (100 + (T-BT)*4*WT + (30-BH)*WH – 200*(P-BP)*WP) %
“30-BH” should be “BH-H”
the final formula is: Watering Percentage = (100 + (T – BT) * 4 * WT + (BH – H) * WH – 200 * (P – BP) * WP) %

The weighting part of the formula seems wrong, the result for the given example values is 1300%, expected are 112%

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