I grabbed more messages:
z_t_cnt=10,p=0.054,rr=11.416,d=0.061,pos=46.5,9.3
z_t_cnt=11,p=0.046,rr=12.626,d=0.055,pos=40.1,11.9
z_t_cnt=12,p=0.046,rr=13.021,d=0.054,pos=44.5,15.0
avr_rr=12.354209,avr_d_rr=0.222
X35.0 Y31.0,z_c= 0.140 ,z_d=0.054
PX35.0 Y31.0,prev_z_c_diff= 0.010
z_t_cnt=13,p=-0.059,rr=13.228,d=0.053,pos=79.6,9.4
z_t_cnt=14,p=-0.064,rr=14.368,d=0.049,pos=75.2,13.7
z_t_cnt=15,p=-0.063,rr=14.881,d=0.047,pos=77.1,15.3
avr_rr=14.158761,avr_d_rr=0.241
X73.0 Y31.0,z_c= 0.024 ,z_d=0.047
PX73.0 Y31.0,prev_z_c_diff= 0.001
z_t_cnt=16,p=-0.122,rr=10.823,d=0.065,pos=112.9,5.9
z_t_cnt=17,p=-0.127,rr=12.077,d=0.058,pos=111.0,2.3
z_t_cnt=18,p=-0.128,rr=11.905,d=0.059,pos=110.6,3.6
avr_rr=11.601523,avr_d_rr=0.216
X111.0 Y31.0,z_c= -0.029 ,z_d=0.059
PX111.0 Y31.0,prev_z_c_diff= 0.014
z_t_cnt=19,p=-0.132,rr=11.737,d=0.060,pos=152.9,-0.7
z_t_cnt=20,p=-0.126,rr=12.438,d=0.056,pos=148.9,5.5
z_t_cnt=21,p=-0.126,rr=12.821,d=0.055,pos=148.4,7.4
avr_rr=12.331805,avr_d_rr=0.163
X149.0 Y31.0,z_c= -0.032 ,z_d=0.055
PX149.0 Y31.0,prev_z_c_diff= 0.012
z_t_cnt=22,p=-0.059,rr=13.021,d=0.054,pos=182.8,14.0
z_t_cnt=23,p=-0.065,rr=14.368,d=0.049,pos=185.3,14.6
z_t_cnt=24,p=-0.063,rr=15.152,d=0.046,pos=182.9,16.2
avr_rr=14.180056,avr_d_rr=0.324
X187.0 Y31.0,z_c= 0.023 ,z_d=0.046
PX187.0 Y31.0,prev_z_c_diff= 0.004
z_t_cnt=25,p=0.027,rr=11.905,d=0.059,pos=216.3,15.0
z_t_cnt=26,p=0.018,rr=11.111,d=0.063,pos=228.8,14.7
z_t_cnt=27,p=0.020,rr=12.077,d=0.058,pos=223.2,16.0
avr_rr=11.697723,avr_d_rr=0.656
X225.0 Y31.0,z_c= 0.118 ,z_d=0.058
PX225.0 Y31.0,prev_z_c_diff= 0.005
z_t_cnt=28,p=0.050,rr=11.416,d=0.061,pos=51.6,60.3
z_t_cnt=29,p=0.038,rr=10.040,d=0.070,pos=38.5,64.8
z_t_cnt=30,p=0.040,rr=10.684,d=0.066,pos=42.9,65.9
avr_rr=10.713149,avr_d_rr=0.907
X35.0 Y72.0,z_c= 0.146 ,z_d=0.066
PX35.0 Y72.0,prev_z_c_diff= -0.004
sensitive test freq=14.0Hz
strain 1 sensitivity = 0.001038,p=-1.626,Vs=1791.6
strain 2 sensitivity = 0.001090,p=-1.627,Vs=1789.6
strain 3 sensitivity = 0.001013,p=-1.583,Vs=1790.4
z_t_cnt=31,p=-0.009,rr=10.684,d=0.066,pos=74.8,53.2
z_t_cnt=32,p=-0.024,rr=10.417,d=0.067,pos=66.9,49.5
z_t_cnt=33,p=-0.014,rr=10.965,d=0.064,pos=73.0,54.0
avr_rr=10.688447,avr_d_rr=0.270
X73.0 Y72.0,z_c= 0.090 ,z_d=0.064
PX73.0 Y72.0,prev_z_c_diff= 0.004
z_t_cnt=34,p=-0.053,rr=13.889,d=0.050,pos=112.7,48.0
z_t_cnt=35,p=-0.055,rr=14.620,d=0.048,pos=113.6,53.3
z_t_cnt=36,p=-0.055,rr=14.881,d=0.047,pos=114.2,53.5
avr_rr=14.463243,avr_d_rr=0.139
X111.0 Y72.0,z_c= 0.032 ,z_d=0.047
PX111.0 Y72.0,prev_z_c_diff= 0.003
z_t_cnt=37,p=-0.080,rr=13.441,d=0.052,pos=149.2,51.7
z_t_cnt=38,p=-0.084,rr=13.228,d=0.053,pos=149.6,55.6
z_t_cnt=39,p=-0.089,rr=13.021,d=0.054,pos=151.4,57.5
avr_rr=13.229736,avr_d_rr=0.210
X149.0 Y72.0,z_c= 0.005 ,z_d=0.054
PX149.0 Y72.0,prev_z_c_diff= 0.006
z_t_cnt=40,p=-0.041,rr=13.889,d=0.050,pos=185.1,51.9
z_t_cnt=41,p=-0.043,rr=14.368,d=0.049,pos=187.9,55.4
z_t_cnt=42,p=-0.041,rr=14.368,d=0.049,pos=184.8,55.9
avr_rr=14.208176,avr_d_rr=0.053
X187.0 Y72.0,z_c= 0.048 ,z_d=0.049
PX187.0 Y72.0,prev_z_c_diff= 0.002
z_t_cnt=43,p=0.036,rr=11.111,d=0.063,pos=217.1,61.8
z_t_cnt=44,p=0.028,rr=10.684,d=0.066,pos=231.1,63.2
z_t_cnt=45,p=0.032,rr=11.905,d=0.059,pos=222.2,65.0
avr_rr=11.233212,avr_d_rr=0.509
X225.0 Y72.0,z_c= 0.131 ,z_d=0.059
PX225.0 Y72.0,prev_z_c_diff= 0.005
z_t_cnt=46,p=0.039,rr=11.574,d=0.060,pos=44.4,100.1
z_t_cnt=47,p=0.029,rr=9.921,d=0.071,pos=36.4,104.7
z_t_cnt=48,p=0.034,rr=10.684,d=0.066,pos=43.0,102.5
avr_rr=10.726158,avr_d_rr=1.088
X35.0 Y113.0,z_c= 0.139 ,z_d=0.066
PX35.0 Y113.0,prev_z_c_diff= -0.001
z_t_cnt=49,p=-0.044,rr=11.261,d=0.062,pos=76.8,94.3
z_t_cnt=50,p=-0.050,rr=11.737,d=0.060,pos=74.9,100.9
z_t_cnt=51,p=-0.047,rr=12.626,d=0.055,pos=77.1,99.7
avr_rr=11.874871,avr_d_rr=0.250
X73.0 Y113.0,z_c= 0.048 ,z_d=0.055
PX73.0 Y113.0,prev_z_c_diff= -0.013
sensitive test freq=14.0Hz
strain 1 sensitivity = 0.001017,p=-1.630,Vs=1806.2
strain 2 sensitivity = 0.001086,p=-1.632,Vs=1795.5
strain 3 sensitivity = 0.001011,p=-1.585,Vs=1802.8
z_t_cnt=52,p=-0.081,rr=13.889,d=0.050,pos=114.5,97.8
z_t_cnt=53,p=-0.082,rr=13.889,d=0.050,pos=115.7,99.4
z_t_cnt=54,p=-0.083,rr=13.889,d=0.050,pos=115.9,100.5
avr_rr=13.888888,avr_d_rr=0.000
X111.0 Y113.0,z_c= 0.008 ,z_d=0.050
PX111.0 Y113.0,prev_z_c_diff= 0.005
z_t_cnt=55,p=-0.072,rr=13.441,d=0.052,pos=151.0,98.2
z_t_cnt=56,p=-0.076,rr=13.228,d=0.053,pos=152.0,100.9
z_t_cnt=57,p=-0.075,rr=13.889,d=0.050,pos=151.7,101.8
avr_rr=13.519088,avr_d_rr=0.265
X149.0 Y113.0,z_c= 0.015 ,z_d=0.050
PX149.0 Y113.0,prev_z_c_diff= 0.003
z_t_cnt=58,p=-0.029,rr=12.438,d=0.056,pos=194.5,103.1
z_t_cnt=59,p=-0.023,rr=12.438,d=0.056,pos=192.7,103.3
z_t_cnt=60,p=-0.023,rr=12.077,d=0.058,pos=191.0,102.2
avr_rr=12.317638,avr_d_rr=0.160
X187.0 Y113.0,z_c= 0.075 ,z_d=0.058
PX187.0 Y113.0,prev_z_c_diff= 0.001
z_t_cnt=61,p=0.045,rr=10.163,d=0.069,pos=220.5,106.5
z_t_cnt=62,p=0.035,rr=9.158,d=0.076,pos=231.8,110.1
z_t_cnt=63,p=0.039,rr=9.804,d=0.071,pos=226.9,110.1
avr_rr=9.708012,avr_d_rr=0.702
X225.0 Y113.0,z_c= 0.150 ,z_d=0.071
PX225.0 Y113.0,prev_z_c_diff= -0.015
z_t_cnt=64,p=0.023,rr=8.865,d=0.079,pos=40.6,145.4
z_t_cnt=65,p=0.013,rr=8.503,d=0.082,pos=33.3,150.9
z_t_cnt=66,p=0.013,rr=7.937,d=0.088,pos=33.7,149.8
avr_rr=8.435052,avr_d_rr=0.453
X35.0 Y154.0,z_c= 0.142 ,z_d=0.088
PX35.0 Y154.0,prev_z_c_diff= 0.017
z_t_cnt=67,p=-0.051,rr=10.965,d=0.064,pos=77.4,141.2
z_t_cnt=68,p=-0.056,rr=11.737,d=0.060,pos=75.9,148.9
z_t_cnt=69,p=-0.053,rr=12.626,d=0.055,pos=79.5,145.6
avr_rr=11.776090,avr_d_rr=0.283
X73.0 Y154.0,z_c= 0.043 ,z_d=0.055
PX73.0 Y154.0,prev_z_c_diff= -0.009
z_t_cnt=70,p=-0.086,rr=12.077,d=0.058,pos=116.4,145.9
z_t_cnt=71,p=-0.089,rr=11.574,d=0.060,pos=117.2,148.5
z_t_cnt=72,p=-0.090,rr=12.255,d=0.057,pos=116.9,149.9
avr_rr=11.968759,avr_d_rr=0.431
X111.0 Y154.0,z_c= 0.007 ,z_d=0.057
PX111.0 Y154.0,prev_z_c_diff= -0.002
sensitive test freq=14.0Hz
strain 1 sensitivity = 0.001005,p=-1.629,Vs=1806.0
strain 2 sensitivity = 0.001093,p=-1.630,Vs=1791.7
strain 3 sensitivity = 0.001017,p=-1.583,Vs=1801.2
z_t_cnt=73,p=-0.042,rr=12.626,d=0.055,pos=153.2,150.1
z_t_cnt=74,p=-0.045,rr=12.438,d=0.056,pos=153.7,154.2
z_t_cnt=75,p=-0.057,rr=13.228,d=0.053,pos=156.4,162.1
z_t_cnt=76,p=-0.044,rr=13.441,d=0.052,pos=153.1,150.5
z_t_cnt=77,p=-0.045,rr=13.441,d=0.052,pos=152.8,150.9
avr_rr=13.034661,avr_d_rr=0.157
X149.0 Y154.0,z_c= 0.047 ,z_d=0.052
PX149.0 Y154.0,prev_z_c_diff= -0.010
z_t_cnt=78,p=0.027,rr=10.965,d=0.064,pos=184.2,147.6
z_t_cnt=79,p=0.017,rr=10.040,d=0.070,pos=193.9,156.7
z_t_cnt=80,p=0.021,rr=10.823,d=0.065,pos=190.4,153.3
avr_rr=10.609196,avr_d_rr=0.688
X187.0 Y154.0,z_c= 0.125 ,z_d=0.065
PX187.0 Y154.0,prev_z_c_diff= 0.000
z_t_cnt=81,p=0.078,rr=7.937,d=0.088,pos=226.4,150.2
z_t_cnt=82,p=0.069,rr=8.170,d=0.086,pos=235.6,156.9
z_t_cnt=83,p=0.072,rr=8.591,d=0.081,pos=231.9,156.3
avr_rr=8.232503,avr_d_rr=0.120
X225.0 Y154.0,z_c= 0.193 ,z_d=0.081
PX225.0 Y154.0,prev_z_c_diff= -0.010
z_t_cnt=84,p=-0.011,rr=7.246,d=0.097,pos=41.5,190.1
z_t_cnt=85,p=-0.025,rr=6.614,d=0.106,pos=28.9,203.1
z_t_cnt=86,p=-0.023,rr=6.562,d=0.107,pos=31.3,201.0
avr_rr=6.807271,avr_d_rr=0.375
X35.0 Y195.0,z_c= 0.124 ,z_d=0.107
PX35.0 Y195.0,prev_z_c_diff= 0.001
z_t_cnt=87,p=-0.076,rr=10.965,d=0.064,pos=79.4,186.9
z_t_cnt=88,p=-0.080,rr=10.823,d=0.065,pos=79.3,193.0
z_t_cnt=89,p=-0.079,rr=11.416,d=0.061,pos=81.0,190.9
avr_rr=11.067650,avr_d_rr=0.211
X73.0 Y195.0,z_c= 0.022 ,z_d=0.061
PX73.0 Y195.0,prev_z_c_diff= -0.010
z_t_cnt=90,p=-0.099,rr=11.905,d=0.059,pos=117.2,191.9
z_t_cnt=91,p=-0.103,rr=11.737,d=0.060,pos=118.2,195.9
z_t_cnt=92,p=-0.104,rr=11.416,d=0.061,pos=117.8,195.9
avr_rr=11.685793,avr_d_rr=0.236
X111.0 Y195.0,z_c= -0.003 ,z_d=0.061
PX111.0 Y195.0,prev_z_c_diff= 0.003
z_t_cnt=93,p=-0.071,rr=14.620,d=0.048,pos=152.6,197.4
z_t_cnt=94,p=-0.070,rr=14.368,d=0.049,pos=152.4,194.7
z_t_cnt=95,p=-0.069,rr=14.620,d=0.048,pos=151.6,192.5
avr_rr=14.535861,avr_d_rr=0.196
X149.0 Y195.0,z_c= 0.019 ,z_d=0.048
PX149.0 Y195.0,prev_z_c_diff= -0.012
sensitive test freq=14.0Hz
strain 1 sensitivity = 0.001007,p=-1.629,Vs=1805.5
strain 2 sensitivity = 0.001083,p=-1.630,Vs=1789.6
strain 3 sensitivity = 0.001012,p=-1.583,Vs=1799.5
z_t_cnt=96,p=-0.008,rr=10.684,d=0.066,pos=188.8,193.7
z_t_cnt=97,p=-0.017,rr=9.690,d=0.072,pos=197.8,203.8
z_t_cnt=98,p=-0.016,rr=9.804,d=0.071,pos=196.1,201.8
avr_rr=10.059202,avr_d_rr=0.577
X187.0 Y195.0,z_c= 0.095 ,z_d=0.071
PX187.0 Y195.0,prev_z_c_diff= -0.002
z_t_cnt=99,p=0.108,rr=7.123,d=0.098,pos=224.0,193.7
z_t_cnt=100,p=0.091,rr=6.313,d=0.111,pos=241.6,216.3
z_t_cnt=101,p=0.093,rr=6.361,d=0.110,pos=238.4,207.8
avr_rr=6.598987,avr_d_rr=0.460
X225.0 Y195.0,z_c= 0.243 ,z_d=0.110
PX225.0 Y195.0,prev_z_c_diff= -0.001
z_t_cnt=102,p=-0.057,rr=6.510,d=0.108,pos=47.6,230.8
z_t_cnt=103,p=-0.069,rr=6.410,d=0.109,pos=39.9,250.0
z_t_cnt=104,p=-0.069,rr=6.127,d=0.114,pos=39.5,247.8
avr_rr=6.349375,avr_d_rr=0.181
X35.0 Y236.0,z_c= 0.086 ,z_d=0.114
PX35.0 Y236.0,prev_z_c_diff= -0.012
z_t_cnt=105,p=-0.136,rr=8.251,d=0.085,pos=78.0,230.1
z_t_cnt=106,p=-0.143,rr=8.013,d=0.087,pos=74.3,240.8
z_t_cnt=107,p=-0.144,rr=8.091,d=0.087,pos=74.3,241.0
avr_rr=8.118087,avr_d_rr=0.150
X73.0 Y236.0,z_c= -0.017 ,z_d=0.087
PX73.0 Y236.0,prev_z_c_diff= 0.001
z_t_cnt=108,p=-0.152,rr=9.579,d=0.073,pos=117.1,239.2
z_t_cnt=109,p=-0.155,rr=10.549,d=0.066,pos=117.8,245.4
z_t_cnt=110,p=-0.156,rr=10.163,d=0.069,pos=117.6,246.6
avr_rr=10.096556,avr_d_rr=0.279
X111.0 Y236.0,z_c= -0.047 ,z_d=0.069
PX111.0 Y236.0,prev_z_c_diff= -0.004
z_t_cnt=111,p=-0.114,rr=9.804,d=0.071,pos=151.9,238.2
z_t_cnt=112,p=-0.120,rr=10.417,d=0.067,pos=154.1,248.4
z_t_cnt=113,p=-0.120,rr=9.470,d=0.074,pos=154.0,248.5
avr_rr=9.896762,avr_d_rr=0.489
X149.0 Y236.0,z_c= -0.006 ,z_d=0.074
PX149.0 Y236.0,prev_z_c_diff= -0.002
z_t_cnt=114,p=-0.032,rr=9.158,d=0.076,pos=190.7,238.1
z_t_cnt=115,p=-0.043,rr=9.158,d=0.076,pos=200.0,259.1
z_t_cnt=116,p=-0.036,rr=9.470,d=0.074,pos=192.9,245.2
avr_rr=9.261572,avr_d_rr=0.069
X187.0 Y236.0,z_c= 0.078 ,z_d=0.074
PX187.0 Y236.0,prev_z_c_diff= -0.014
sensitive test freq=14.0Hz
strain 1 sensitivity = 0.001025,p=-1.627,Vs=1815.0
strain 2 sensitivity = 0.001079,p=-1.631,Vs=1792.4
strain 3 sensitivity = 0.001002,p=-1.583,Vs=1800.8
z_t_cnt=117,p=0.097,rr=5.556,d=0.126,pos=233.4,268.7
z_t_cnt=118,p=0.095,rr=5.828,d=0.120,pos=234.4,265.0
z_t_cnt=119,p=0.092,rr=5.787,d=0.121,pos=236.7,267.6
avr_rr=5.723366,avr_d_rr=0.048
X225.0 Y236.0,z_c= 0.253 ,z_d=0.121
PX225.0 Y236.0,prev_z_c_diff= -0.009
G29:home pos comp err: 0.016mm
G29 SUCCESS
The ones starting with z_t_cnt occur each time the nozzle hits the bed. It seems to be data averaged from the 3 pressure sensors (d=displacement at pos=position with p=pitch and rr=rolling?) and the last d measured in each batch becomes the z_d in the X/Y/z_c/z_d message. In the following message, the prev_z_c_diff is the difference with the same spot in previous ABL.
So I guess the interesting value is just the z_c after all.
Would be nice if someone else could capture his ABL MQTT logs to see what happens with a different bed