Just in case the symbols do not appear correctly they are d, upper case delta, lower case delta, and lower case del. Also, what is the difference between dy, Δy, δy and ∂y when they are on their own? I think δy (lower case delta) is a infinitesimally small change in y, where as Δy (uppercase delta) is just y2 - y1 where the difference can be much larger. Is this correct? Also how does this differ from dy and ∂y? Note: I understand calculus and rates of change, I just do not know the difference between these different symbols and forms of differentials.