The table below shows data recorded during an oedometer test on a soil sample for an increment of vertical stress of $200$kPa. The initial sample thickness is $20mm.$

$\backslash$table$[[$Time $($min$),0,0\mathrm{.}25,1,4,9,16,36,64,100],[$Deformation $($mm$),0,0\mathrm{.}30,0\mathrm{.}35,0\mathrm{.}49,0\mathrm{.}61,0\mathrm{.}73,0\mathrm{.}90,0\mathrm{.}95,0\mathrm{.}97]]$

After $24$ hours the deformation was negligible and the void ratio was $1\mathrm{.}20,$ corresponding to a sample height of $18\mathrm{.}2mm.$ Determine $c_v$ using the root time and log time methods.