i think there are 2 things to consider:
- if the fruit is still developing, the size of the fruit may not be a good indicator of apple vs crab apple. so you might need a secondary field to record whether the fruit was ripe or not (or unknown), or request the size only from ripe fruit.
- if you want to be able to query for sets of observations, it might be best to set up this field as a set of ranges (ex. up to 5cm / greater than 5cm / not able to determine), rather than allowing any numeric input. (the system doesn’t have a built-in way to sort based on observation values. so you’d have to do that outside of the system.)