help understand a piece of input code for particle shrinkage

Could somebody help me to understand this piece of input code used for temperature trigerred shrinkage code

#set particle temperature for half the bed
1. region halfbed block 0 INF INF INF INF INF units box
2. set region halfbed property/peratom Temp 800.

#define particle shrinkage based on temperature
#particles shrink with constant rate if temperature > 500 °
3. variable shrinkevery equal 20
4. variable TempTresh equal 500.
5. variable rate equal 0.9995
6. variable tresh atom f_Temp>${TempTresh}
7. compute rad all property/atom radius
8. variable d_shrunk atom 2.*c_rad*(v_tresh*${rate}+(1.-v_tresh))
9. fix grow all adapt ${shrinkevery} atom diameter d_shrunk

#run to see heat transfer w/ shrinkage
run 50000 upto

I have the question in line no. 6. , 8. and 9.
What is the value of variable "tresh" or v_tresh? Is it the individual Temperature list of group of atoms which is greater than "${TempTresh}"? In that case the formula in line 8. seems to not follow the dimensional consistency. Please explain line by line of this code, if possible.

Thanks