# 6.6. Standards for Calculating Hourly, Daily and Annual Means

INTERMAGNET requires that all mean values be calculated using the rules described in the next sections.

## 6.6.1. Hourly Mean Values

The hourly mean values must be produced following the IAGA rules:

Arithmetic average of the 1-minute data

Centered on the center of the hour (HH:29:30, HH=hour) using 1-minute data 00-59 of the hour

## 6.6.2. Daily Mean Values

The daily mean values must be produced using the following rules:

Arithmetic average of the 1-minute data

Centered on the center of the day (11:59:30) using 1-minute data 00:00-23:59 of the day

## 6.6.3. Annual Mean Values

The annual mean values must be produced using the following rules:

Arithmetic average of the 1-minute data

Centered on the center of the year (02 July 11:59:30 for a regular year, 01 July 23:59:30 for a leap year) using 1-minute data 01 January 00:00- 31 December 23:59 of the year

## 6.6.4. Rule for Missing 1-minute Values

When mean values are to be calculated the question of how to handle missing data arises. For a number of reasons it is difficult to devise a simple objective rule that can be applied to all cases. INTERMAGNET recommends a simple and pragmatic approach: mean or filtered values may be calculated when 90% or more of the values required for calculation are available. This can be interpreted as either 90% of the values or 90% of the weight of the filter. When fewer than 90% of the required values are available the value should be assigned the value used to flag missing data.