Why SIP amount calculator?

SIP amount calculator calculates the investment amount according to their valuation with a regular SIP amount if market in a median valuation.
Generally investor investing money in equity, mutual funds, ETF which is volatile asset, in a regular interval like as monthly, bimonthly, quarterly etc. but for extra rate of reurn over our investment, we have to invest by valuation. Suppose market in a low valuation then investor invest more money like that if market in a high valuation then investor invest less money.
But how we will know that market in a low valuation or in a high valuation. For this we will use 3-years or more historical median data of any valuation ratio like as PE ratio, PBV, Mcap/sales ratio etc which is best for us.

What is the SIP amount step up/ step down calculator formula?

a= Regular SIP amount
b= Median PE ratio or PBV for Regular SIP amount (>0)
c= Current PE ratio or PBV (>0)
Current PE ratio up or down from median PE, x= (c-b)*100/b
SIP amount step up/step down, y
If, x>0
y= a/(c/b)^(1+0.5*0.01*x)
Else,
y= a/(c/b)^(1-2*0.01*x)