[EpiData-list] EpiData - JUMPS involving calculations

I am a new EpiData user. I am creating a data entry screen for anthropometric data.

There are two weight measurements - and a third if the first two differ by +/- 0.5 kg.

How can I incorporate this calculation in the JUMP section of the Add/Revise Checks so

(1) if WT1 - WT2 GE 0.5 OR LE -0.5 go to WT3 (2) else go to HT1 [the next field]

Thank you.