calculating average ratings from a series of review fields
Something like this should work:

{% set reviews = craft.entries.section('reviews').relatedto(entry) %}
{% set value = 0 %}
{% set condition = 0 %}
{% set reception = 0 %}
{% set count = 0 %}
{% for review in reviews %}
    {% set value = value + review.value %}
    {% set condition = condition + review.condition %}
    {% set reception = reception + review.reception %}
    {% set count = loop.index %}
{% endfor %}
{% set averageValue = (value / count)|round(1, 'floor') %}
{% set averageCondition = (condition / count)|round(1, 'floor') %}
{% set averageReception = (reception / count)|round(1, 'floor') %}