What is this formula? Used to convert quarterly basis data to monthly basis

Hi all,

I am new to this forum and I wish someone can help me here. Would someone help me to identify the name of formula used below? Thanks!

Every quarter, we receive projection from other department and their projection are in quarterly basis, I have to convert the quarterly data into monthly data, and we use the formula below for conversion.

For example, if we want to get April 2018 (First month result), May 2018 (Second month result) and June 2018 (Third month result)monthly data, then we will use 2018Q1 (Last Quarter value), 2018Q2 (This Quarter value) and 2018Q3 (Next Quarter value), then apply them into formula below: pic1.jpg
It looks like some sort of interpolation formula, but I don't see why the third month projection isn't the same as the next quarter projection.